I've taken the basic idea (gameplay, not storyline) from cave story:
http://agtp.romhack.net/doukutsu.html

Maybe a nice one for you to play.

About pursuing this idea... I'm nearly finished with my studies (IT study) and after I get my diploma it's off to find a job first.... Maybe, just maybe I'll actually make this game.

Nice thing about such a storyline with this amount of characters (grows as the storyline progresses) is the multiplayer ability...
All boosters (better weapons, more speed, better jump, etc...) will form your character in a multiplayer battle. Something like soldat came to mind, but I think I'll rule out mouse control. If someone definitely HAS to aim with a gun, a liero type crosshair should suffice.