Portfolio managers - is there an upper limit to the number of projects that can be managed in a portfolio?

Context: I am cleaning up a thin portfolio of about ~70ish tech projects ($50K to 100K USD each) and I think I need to scale it to 200 to 700 projects within the next 12 months.  

Details: the PMs & projects are all external and PM capabilities are all over the place, and we are only managing time and quality, cost is fixed.  Think of very simple binary milestone evaluation: did you hit the timeline with quality?  If yes, get paid.  If no, thinly manage the exception: if it cannot be quickly corrected, cancel the project.

As designed today, PMs need to submit updates every fortnight, milestones are monthly, and all communications are managed via telegram chats (omg!).  

Its all transactional - and I need to clean it up and put AI agents in place - somehow.