My comments on the "Speculation about the Nature of the 11 Planet Types" (please note that these mostly represent my opinion, and of course you are in no way obliged to shift your vision in a way to better align with mine):
Inner System:
- Heliosal Desert:
* If it's approximately the size and mass of Mercury at approximately the same distance from its star, and its star is about the same mass as our Sun, then the gravitational attraction of objects on the planet to the star would be about 1% of the strength of the attraction of those same objects to the planet. While this is about 20 times greater than the effect on Earth, it probably isn't terribly significant in comparison to the effects of the atmospheric currents which would likely be generated by the thermal gradient between the day side and night side of the planet, which could cause dangerous levels of wind shear for tall structures and airborne vehicles; additionally, the issues caused by the interaction of solar and planetary gravity would be at their worst at the day/night boundary, which is an area that you indicate that you expect that any species inhabiting the planet would avoid
* Structures on the planet large enough to make a noticeable 'spike' on the planet's surface (at least when viewed from orbit or beyond) are likely to be of a height in excess of 4% of the planet's radius (if you disagree, I suggest plotting a series of ellipses of varying eccentricity, and picking which one you think would create a noticeable spike if used as the bounding box for a tower). On a Mercury-sized planet, this is equivalent to a 100km-tall skyscraper at the equator, which if transplanted onto Earth would be a structure which reaches into the thermosphere and has roughly 33,000 stories. Just something to think about if you want 'spiky' planets
* Another issue for the really tall structures to overcome is their increased vulnerability to earthquakes, which a world with a nearly molten face might be expected to have plenty of. It might be too dangerous to build such massive structures, though this could provide an additional impetus to get into space
* If these are among the smaller life-bearing planets, they should be relatively easy to attain spaceflight on, as they are relatively low-gravity and might be expected to have similar resources as are present on other rocky planets, though fossil fuels could be more difficult to come by
* You might be able to generate energy based on the thermal gradient between the day and night side of the planet, or even between parts of the night side closer to the day side and parts of the night side further away, if the temperature gradient is severe enough. You'll also likely have near-constant high winds, if you wanted to produce power via wind turbines
- Iron Silicate:
* If the Heliosal Deserts aren't melting, this probably isn't either. Rocky planets like Earth and Mercury are mostly iron and silicon anyways
* If it's approximately equal in size and mass to Mercury at approximately the same distance from its star as Mercury is from the Sun, and the star is similar to the Sun in mass, then there's only up to about a 1% increase in nominal weight when on the side facing away from the star, and up to about a 1% decrease in nominal weight when on the side facing the sun (the 1% peaks at the noon and midnight positions). At the day/night boundary it's more interesting, because it should feel something like being on a 1-degree slope
* It'd need to be spinning very fast before there'd be too much concern about buildings shearing due to planetary rotation, unless the building's height is some significant fraction of the planet's radius
* Structural strength issues with regards to gravitational variation are more likely to be caused by changes in the direction of 'down' as the planet rotates than by the change in the apparent weight of the structure and its occupants. Factors of safety on structures on Earth are rarely less than 10% (meaning that most structures are designed to withstand a load at least 10% greater than that which they are rated to), with the only notable exceptions being those in which weight and cost are significant concerns (airplanes are an example of this, mostly due to weight)
- Molten:
* Unlikely to be a good mining prospect, unless there's something here that simply cannot be fabricated on an economically useful scale from materials sourced from anywhere else. It's just too expensive to design and build systems that can operate under the high temperature, high radation conditions, and there's little to no chance of recovering equipment after a failure
* If something evolved to live in lava and hasn't adapted to living exposed to atmosphere, it's going to have an extremely difficult time getting off planet, as molten rock is very heavy and will therefore require a significant amount of energy to lift off the planet
Habitable Zone:
* Don't really have much to say here, aside from that a sufficiently large Transitional Desert world could have a reasonably dense atmosphere, though the composition might be significantly different from that of Earth; the lack of a significant atmosphere on Mars is more due to the lower gravity than to its desert-like qualities
Outer System:
- Hypertonic Gas Giant:
* doesn't matter that the core is resource-rich and massive - there's probably not anything there that cannot be found in the asteroid belt or on a planet/moon similar to the species' homeworld, which means that it's likely not economically feasible to design and build a mining operation on the gas giant; same goes for colonization efforts, as unless you evolved for similar conditions it's just too dangerous, with even minor accidents being capable of destroying significant portions of a colony (especially a new colony)
* any species that evolves underground in the core and which isn't adapted to high pressure is going to go extinct the first time something breaks open a tunnel, unless they were aware of the possibility and prepared for it. Probably wouldn't need pressure suits on their own planet's surface, unless it's to keep the pressure up at the same levels as it is in their tunnels
* any species native to the planet might be able to outpace all others in terms of available resources, but they're going to have to pay a significant cost getting those resources off the planet if they want to use them - high winds at the surface make launching things dangerous, and you need significant amounts of fuel to attain, and eventually break, orbit, far more than would be necessary around an Earth-like planet, although I suppose it might be possible to do something like a hot air balloon for getting into the upper atmosphere, and then launch the rest of the way from there (though I expect this would be dangerous unless your balloon material and payload is very resistant to flying debris or being blown into a nearby mountain side)
* I would tend to expect that any animals living on the surface of the planet would tend towards small sizes, limiting the pressure gradient between the top and bottom of the animal and additionally minimizing their sail area, which would protect them somewhat from the high winds; this would give you something more ant-like than godzilla-like, in my opinion
- Gauss Gas Giant
* same kinds of stuff as for the hypertonic gas giant and dense turbulent
* strong EM fields might make electrical systems difficult or dangerous to manufacture/operate, depending on just how strong the fields are, and may cause issues with developing some of the instruments that we have on Earth today; additionally, the noise floor would be much higher, which would tend to require higher power components. The inhabitants might have some trouble developing low-power systems that can be launched from their home planet
- Equatorial Ring:
* not much to say that isn't in one of the other gas giant world comments
Ice Belt:
- Ice Dwarf:
* whether or not you'd maximize the surface area for maximizing absorption is debatable - increased surface area also means increased radiative losses, and so livable areas might well end up being made to fit into minimum-surface area shapes like spheres, with climate control handled by radiator vanes and solar panels (or some form of reactor) in sections branching off of the habitat.
* while I agree that it's unlikely that life would evolve in such a location, I would say that for any space-faring species seeking to establish an outpost, such a location is not significantly less inhabitable than a space station of some kind which wasn't established on any pre-existing body. If you chose to build something out here, it might even be more practical to build on or around an Ice Dwarf than otherwise simply because the Ice Dwarf might provide you a nearby source of resources (such as water ice, which if present in reasonable quantities on the Ice Dwarf would be one less thing that you needed to ship out to the station or find on a (relatively) nearby body.
* any species that does evolve on an Ice Dwarf should have a relatively easy time achieving spaceflight, assuming that their world has similarly available natural resources as a more conventional homeworld, as getting off planet should be much easier. However, they should have fairly significant troubles colonizing (or even visiting) anything with a stronger gravitational field or a higher pressure (or extant) atmosphere
* if there are available resources in an Ice Dwarf, this should be a relatively attractive mining target, as lower gravity and little to no atmosphere means it's not particularly difficult to set up and operate an extraction operation or ship the resources off site, though the total distance that the resources would need to be shipped may pose a problem
- Dense Turbulent:
* sorry, but this is a very bad mining prospect, unless what you're mining are particles in a ring around the planet or gases in the upper atmosphere. Just making something that will work reliably in the planet for any worthwhile length of time would be enormously expensive, and then you come to the issue of getting whatever you're mining off of the planet. Cloud City on Bespin is a nice concept, but unless there's something that practically cannot be had anywhere else, it's not an economically feasible concept
* mining any moons around one of these, on the other hand, could work, as could harvesting the ejecta from volcanic eruptions (though the moon would have to either have a very large eruption or very frequent eruptions, or frequent large meteor impacts, for harvesting ejecta to be a practical mining operation
* it's not particularly likely that anything is going to get 'sucked up' off of a moon's surface, not without that object having a significant initial velocity (such as debris might have after a volcanic eruption or meteor impact). It could, however, make launching craft into orbit somewhat easier than it would be to perform the same operation on a similarly-sized planet, but probably not terribly much cheaper
* if there is an issue with the planet's gravity 'sucking' things off of the surface of the moon, the moon either will not have an atmosphere, or its atmosphere will be at least partially within the planet's atmosphere
Side note:
As far as space-based mining prospects go, I'd say that unless the Hydrals more or less depleted the readily accessible asteroids in any belt inside the outermost planetary orbit, then most likely those asteroids would be the most economically viable targets (same goes for comets, if available). Next would come small moons and dwarf planets, starting with the ones in the most convenient locations, and graduating to larger bodies as viable mining locations become depleted (preferably, with moons and dwarf planets, you'd start either with things which only orbit the local star, or with ones which only orbit your homeworld or a small planet, and then move on to bodies orbiting the larger, and probably more distant, worlds). Another likely 'mining' target would be to scavenge any derelect vessels/stations, as these are likely to be of significant scientific value and are additionally reasonably concentrated sources of refined, high-value materials useful for spaceships, though potentially with the issue of any remaining automated defense systems or dangers caused by whatever left the ship derelect. Additionally, if diplomacy between spacefaring species in the system runs similarly to that between seafaring nations on Earth, the salvaging of destroyed warships may be a criminal offense (as destroyed warships remain the property of the nation whose flag they flew when they were destroyed and are often considered to be the tombs of those who died with the vessel) or may be impractical due to the debris being too scattered by the destruction. As a result, the debris fields from large battles may end up becoming valuable resources and contested locations if made eligible for mining, even if not over a planet of any particular value, and could offer a method of provoking a war if the debris field is considered a tomb or monument and scavenging it is seen as desecration by some parties.
Also, a spreadsheet with the numbers for planet eccentricity, and a little graph of 90-degree arcs showing the bounds of the various eccentricities that I listed in the table (chart is on sheet 2). You'll need something compatible with Excel 2007 to view the spreadsheet:
https://www.dropbox.com/s/o2ximfq6llo286t/PlanetsGravityEccentricity.xlsx
