As per title.

Since you've mentioned how you'll be pulled away from the project in some capacity, would code contributions on GitHub be cool with you, provided proper Git etiquette is followed (branching and pull requests)? What about art/animation/sound/music?

depend on what contributions are made. when it comes to anything visual like sprites ect if it matches my style then maybe. sound track are totally acceptable if you find a good track that isn't copyrighted. as for code contributions, those are also open so long as its a improvement to the current code or makes something more efficient? it depends on the contribution. just contact me about it and depending on what it is ill give the go ahead. my code is open source and free to modify so go crazy.