Hey Valsi!
Sorry I took so long to answer. Its been a hectic week:
1) You can use any open source tools or assets
2) Any engine you choose is permissible. Even one you've built yourself. What's important is that its clearly an 'engine' and not a 'prototype' or unfinished game.
3) Under this theme all genres are permissible.. Only limitation on content would be no offensive content.