i want to know if the following is possible (i'm on the profi-package): can i give people access to my ftp server?
i understand anonymous access is optional, but am i asking for anonymous access? i don't think so.
i want to hand out limited accounts (i.e. upload only, no deleting, with resume activated, with the possibility to create each his own subdirectory).
am i allowed to hand out such accounts? is it technically possible to set up the aforementioned limitations?

Yes, you can.

Yes it is possible. You'll be able to create unlimited subdomains.

If you'll have some new questions please let me know.