I wouldn't set a system yet until I see the boys practice and sort it out from there.
At practice, I'd suggest 1v1's, 2v1's, 3v2's with transition to see who can go to goal, who can defend and who can get up and down. You may end up having a good handful of boys who want to score, or a handful of defendsive minded players. (for indoor, offense is good!
Scheme-wise, I've used 2-3-1 if I have a game breaker up top that can break defenses down. Have also used 1-2-1-2 and 2-1-2-1 giving me four lines vs the opponents 3 lines, which helped getting past each layer up and down the field.
Let us know what you see and ended up with at practice. Hope you end up with some burners!