Haha, I knew I forgot something basic. The Power Cards represent 1 Energy Block, and Energy Blocks are the main method of payment. One face-up or face-down Power Card will at minimum be 1 Energy Block, but certain cards (usually Location Cards) will have the effect of counting as 2 or more Energy Blocks. Of course, the more EBs it counts as, the more specific the applicable situations will be (Tower of Torment, for example, gains a counter that counts as an extra EB each time you perform a Villain Summon under normal game mechanics using that card, but only for the Summon of another Villain, and only once per turn, and only up to 3 counters). This is why you can only place one Power Card per turn. When I'm at my computer, I'll post some sample cards.
Also, re: Boost--
The Boost mechanic does in fact give a different set of stats, but I probably also will have something like "Item Power Card - Gun Maximus: Target Combatant gains 3 Strength Points." In addition, the Focus Zone is merely the easiest method, but not the sole method, of gaining a Boost. Certain effects will also grant Boost; there are a couple of cards that will come into play Boosted if you meet some criterion (like a Paladin might get a Boost if you have other Paladins of the same Theme or Subtype). Examples of the latter might be rare though.
Thanks for your response! I was a bit worried, lol ^_^ -obct