Thanks for your input. I might look at the tool you suggested, but I have no experience in making music, so instead investing time i this regard at the very first time I probably will skip music and learn some other day.
I saw the post you linked to and interpreted it as "you can use your own stuff you previously made" and can't see a statement about third party assets. In the end I don't expect we can't use free fonts or the like, but I'd like to make sure before I waste any time on picking some.