More than anything else, this sounds like a good lesson in why commercial game engines have taken over most of game dev. There are so many things you have to do to make a game, but they're mostly quite common and have lots of off-the-shelf solutions.
That is, any sufficiently mature indie game project will end up implementing an informally specified, ad hoc, bug-ridden implementation of Unity (... or just use the informally specified, ad hoc and bug-ridden game engine called "Unity")
That is, any sufficiently mature indie game project will end up implementing an informally specified, ad hoc, bug-ridden implementation of Unity (... or just use the informally specified, ad hoc and bug-ridden game engine called "Unity")