It's interesting that you bring up tiny touch points in particular being an issue. That's part of the impetus behind my rethinking the entirety of how a player will interact with the game. My other experiences writing mobile apps revealed that touch points centering over small, movable objects *can* work well, but are not ideal, especially on 3.5-4.8 inch screens (it's been less of an issue on tablets, as far as I can tell). The focus for my CSCI studies in college was actually UX, which I always loved deconstructing and analyzing. When I approached the design I was going to use for this game, the first thing I looked at was how to make sure all the touch points were as big as possible while still letting the player see what was going on (or putting hidden menus in places that made sense).
I agree that Knights of Pen and Paper actually does a good job in a lot of ways, and it's probably the closest existing game to what I want, but I still have other ideas for how I want this to work, and how to make the experience (at least, at a basic level) easier for players to use.
As far as game mechanics go, the only question I still have left to answer is what gets "spent" to use "powers." In my original mockup, those things cost HP to do, which works fine on paper and in tabletop playtesting, and even adds an extra level of suspense for the players (I hashed out the battle system by writing it as a tabletop with physical dice rolls first, which will eventually be replaced with a math.Random() analogue), but may not make players feel good in a video game environment. I find HP costs more "hardcore" than having a separate mana pool or similar mechanic, and in my mind are more fun as a resource management mechanic, but only time will tell if that translates as a positive player experience to video games.
Keep in mind, I don't think this'll be easy...very few projects regarding game design are legitimately easy. The tabletop I want to publish as an actual tabletop has taken months longer than I thought it would, but it's also much more complex than the base system I've rigged up for this on multiple levels, more than one of which stem from the nature of the game as modular and extensible...if the most complex thing I'll have to deal with is the programming, I think I have a decent shot at making this work, though an additional programmer would be a welcome addition to the team...