1. Main Menu music isn't really required since there's an add-on for that already and it would probably annoy people who don't want music to begin with. An integrated music player would be nice though.
2. Loading menu and all that is just replaceable gui. If you want something fancier looking, make your own or download one.
3. Engine sound is a definite no. Maybe something more cartoony sounding and more subtle.
4. Spawning system is a pretty good idea.