Illegal? Yes, did you not know that stealing someone else's concept, story, characters, and game engine was illegal? The thing is that no-one really cares a lot of the time if it's not a commercial product. As for hiring someone, YES it costs money, people do not do work for free unless they're really interested or do it for a hobby, so if you want someone to help out for free (which is also quite possible) ask for "Volunteers" or something, if you call it hiring, then they'll want $$. It's not as easy as you think to do good music. It takes time and practice.As for being "very far into development of the game" I'd disagree if that video is the latest that you've got. You don't have a background, or levels, or enemies, and the engine seems really slow and glitchy.
Good luck anyways though.