For the license question above: well, it's not really fair to compare software licenses to artistic works ones. As far as I know, there is no pre-existing license that makes the entire collection of art free culture. Besides, making distribution of the entire work necessary but individual models and textures being disallowed would render the art useless to others as they'd only be able to make clones of the game. CC-BY-SA is a good choice. Even better because you get credited (the freelance artist's most powerful tool is their portfolio!) and anyone who modifies has to release under the same license, benefitting all.