I was under the impression that in order for a game to be libre, you needed
to make the source available.
To your users, yes. Not necessarily to the whole world (although your users
are free to redistribute it).
Contrary to onpon4, I consider the NC and/or the ND components of some
Creative Commons license OK as long as the work is not functional... but,
like she wrote, there should be no software licensed under an NC or ND
license! The GPL or the AGPL probably are the best choices for software you
refuse to see ending up in proprietary software.
And, well, do not hope you will make (much) money first your first graphical
game. It probably won't happen... but the acquired fame can help you to
raise revenues with your second game.
Something else: use an existing engine or, even, consider contributing to an
existing project rather than creating a small game alone.
