@CG_Sky made a tutorial on how to put a game on steam right here:
For the source it’s easy.
- ANY .blend used to create the .EXE is GPL bound! (so use a launcher(a .blend that launches your game.blend will do))
- PYTHON, if you USE any of the Bge API’S then those scripts are BOUND to GPL (99% of gpl can be avoided so search this forum, not gonna explain everything every few days xD)