I personally think you're over complicating things. If you're that untrusting of a staff member they should be uploading into a personal folder only which you can then check the contents before moving them to their proper location. What you're proposing actually doesn't make much sense. Ex: Changing the content is basically the same thing as uploading it. Also, why would anyone need the right to delete something if they weren't also able to upload a file. That would be pretty backwards thinking in my opinion.
They can already upload to a folder without having the ability to change the contents of other items within that folder if you name their rights properly. Ex
r levels */*/*
rw levels citydocks_*
In this case they could read all the levels in the levels folder but only change or delete those that started with citydocks_
(Watch me having had wrote that down wrong since I haven't set rights in so long
)