For most PROs you don’t upload actual music files, but merely register titles and other info. I guess the details of info you have to provide may vary depending on your PRO and their respective process.
Definitely something you should be doing.
Yes. PROs have nothing to do with your AudioJungle exclusivity status. Envato has been allowing PRO registered music for a couple of years.
If your track is registered with a PRO and was properly declared with a cue sheet, or other claiming mechanisms depending on your PRO’s process, then yess indded you should collect royalties.
I’ve read accounts of authors earning quite a lot, and many others nothing. It greatly depends on your placement and whether the track was properly declared by the end user.
The great @RedOctopus wrote a guide about PROs, you guys should check it out, maybe it’ll answer some of the questions you have: