With 10+ years experiencing designing software, my motto is to limit everything and then test at those limits. If you're not limiting things because "why limit this?", then you're going to run into some unhappy conditions in production (and once a user has added 1m songs, it would suck to just delete them out from under them).
Also, you can always raise the limit later if it really matters..
Also, you can always raise the limit later if it really matters..