File Sharing User Limit?
No - people will not connect due to slowness of the storage backing the share long before you'll hit a limit on connected users if there even is one.

I've got 55+ connections to a couple Mac Mini each running just normal sharing and server sharing of various flavors.

I recommend performance mode for any situation where you run a web app or server app or file sharing. The optimizations for single use that protect the system from runaway processes isn't the correct optimization for dozens of people consuming stable services that run as daemons.


https://support.apple.com/en-us/HT202528