Hi,
There is no formal limit but there is unwritten etiquette.
If you post the same thing multiple times the duplicates will be deleted.
If you post a lot of 'listen to me' without getting involved or giving something back, you'll probably be ignored.
Even if you are involved, giving and taking, having ten threads on the first page of the mixing clinic isn't going to look great.
No harm in posting a bunch of songs in one thread, though, or spaced out over time.
Just good manners and sense, really.
If you're posting finished works for promotion, please use the marketing section.
If you're looking for constructive mixing feedback, usually on works in progress, the mp3 clinic is the place.
Welcome to HR.