not sure about 4. I keep a taskforce of Spirecraft at a central location in case something decides to try and hop over the (*Cough* invincible *Cough*) Choke point. Which can help me defend.
That's another totally valid counter. Plus, I think Spirecraft actually synergize with MilComs, while fortresses don't. As always, use what works.
as for 5, why not? with this map style I can EASILY set up two-4 (Depending on positioning) choke points that can brick wall all the enemy forces that try to visit.
As for your note on 5, that's where Spirecraft comes in handy. I set up small choke points over time (Maybe grabbing a wormhole device if the trader passes by) and slowly expand towards the easiest to establish choke point and set a spire city there. Once that's done, I move to the next choke point, having my spire fleet cleave the way, and using spirecraft as "House cleaning" to remove any sticky pests hiding.
Crafting chokepoints on the map is a situational thing. Even if it's easy to do, the amount of territory you need to take can swamp the amount of AIP you can actually handle, even if you're very methodical about how you clear and build the empire up. The main drawback to chokepoints is that, while they're great for funneling the AI into the anvil for smashing, you also have to fight through the exit point to attack the AI homeworld. If taken to extreme, things can get very grindy and thus not fun. For instance, I recently played a 30 hour game to a stalemate at over 1000 AIP because I had taken 50 planets on an 80 planet map (I was going for the 70 planet achievement against an 8/8 AI). The AI was regularly hammering me with fleets of 20k+ ships in addition to exo-waves. While that's an extreme example, it did wonders for teaching me the value of playing
without trying to chokepoint every road on the map, because I had to play serious archipeligo style until I was ready to start connecting the bulk of the empire.
I'll see if I still have any saves of it and show you a few screenshots.