I'll start with health, since that one is less complicated. The suits/tanks idea will work very well, but you'll have the crazy kids who always want to be full health. Then again, you'll always have those guys. If you want to keep the layman being too overly worried about filling up tanks, hide them. Use the color changing suggestion from one of the first pages, and have new tanks change the color of the bar (obviously the numbers would match), then make health psychedelic. You can also have the suit itself be your health indicator on the suit, with the players health-bar telling them that they still have a full bar of health after their suit is out of juice. Something along the lines of how the shield spells currently show damage maybe, but I haven't actually used those xD. But, so long as that health bar is all the way full, only the most OCD and/or cautious explorers will be fretting over it. However, that base health bar has to account for a pretty large majority of health, or else as soon as the suit's power goes down, folks will warp the heck out of there.
What seems optimal to my mind is a system wherein the suits account for around 40% of maximum health at full charge, but are about as hard to make/charge as finding 10-30 regular potions by searching houses. Health improvements would be found rarely inside bosses, (something like their spirit merging with yours), or in high-level treasure rooms. It would not be something you run into often, but would make that base health bar bigger, and be character specific (helps keep you on your toes when death is imminent). The idea of making my health better outside of leveling has a pretty big draw, especially in the current system of static health for the main character. This could make it eventually so that players hang out in levels much higher than theirs because they farmed health, but that's a danger with any system of health-improvement.
As for mana, well, that's a tougher sell. I like the conduit idea. I would say your body can handle a certain amount of spell-power every second coursing through it, and more than your system can handle would not force you to sit around and take damage and wait to cool down (while still allowing that option), but let you keep dishing, but take exponentially increasing amounts of health from you. The visualization for this would be similar to the current magic bar, but you'd start with it empty, then it would fill, once you max it out, the number would keep going up, but the bar would start turning red or bleeding into your health bar (to let you know how much damage you take for casting again, based on your primary mouse button, and allowing for customization). Bleeding into the health bar would require mana to be on the left, so as to bleed into the bottom of health (that way you can easily see how much life you have and if you will die). Your mana bar would decrease fairly quickly, and any damage you incur from burnout would ignore whatever armor you are wearing. I can see that last bit going both ways, but I can't come up with a good lore reason for burning out your armor first unless it's built to help you conduct more.
Example: You fire your mega-spells in rapid succession, burning through your full conduit capacity on the first one, the second you take 20% of your total health, on the third you lose 50% of your total health (now you're at 30%), if you fire a fourth without waiting long enough, you'll toast yourself to death.
Quick thoughts on an ammo system: Make it based on the dust or shards, and have the more complex spells use multiple types of shards. On the spells, just put the maximum number of shots you can fire of that spell. With this system, you have to give the option to always display the current levels of ammo components for the hard-core OCD kids (not on by default of course). Also, I totally like the conduit system better, it's much more, alive, and I hate ammo, everything should be infinigun, I don't use spellscrolls for that very reason.
