Is there a particular reason you're choosing to not use an established ruleset for this? I mean, if it's flexibility you're worried about, just play GURPS, it can handle literally anything you can think of, and it has the advantage of already having been playtested and balanced and the like. Alternatively, tons of people know D&D / Pathfinder, use that ruleset and you'd have an easy time finding folks.

Just a thought.