Consider the following games as points of interest before nailing down specifics in your Game Design (I'm good at making these recommendations, so do try to buy/pirate/emulate them if you haven't played them in your life.)
1. The Lost Vikings
3. Legacy of the Wizard
4. Live a Live (Japan only, though English ROM translations do exist.)
Give special attention to #4 on the list, as outright, the game puts the full cast at your disposal at the front of the game and allows you to play through their various scenarios at your own choosing. Similar to Mega Man, which is kind of loosely also related to your idea regarding the roulette wheel element.
Which, I must say, sounds pretty iffy. How many times must you play it to "land on each character?" I tend to get pretty pissed off when a game forces me into a random thing like that. It's nice as, say, a gimmick to decide what loot/prize/bonus you get of course, but... any thoughts on how that's balanced out?
Not to discourage you and say "It's been done before", just saying... try your "concept" out in real time, see what you liked/didn't like, and add onto it from there. Never go with your first idea... it's usually the fifth or sixth that's the great one.