Favorite lists are personal. However, a group of users can share specific favorite lists
. The effect is that users can stream from (and contribute to) shared favorite lists. Read more
Is it possible to limit download/upload, so only a few users can do it ?
Yes it is.
You - or whoever is the administrator of your AmpJuke installation - can edit the user(s) who should be able to download/upload music.
It's done by selecting "User adm..." (located in the lower left corner, provided you're an administrator).
When editing a user-profile, it is possible to check/uncheck if that individual user can/cannot download/upload.