Hi Oscar,
ok let try in my lab.
Limiting the number of users per port is NOT possible via NAC (RADIUS). On my wishlist is a feature that 802.1x users or system accounts can be used only one time - but this feature is currently NOT available - i hope in future versions.
On important aspect is coming from my co-worker:
(because edge port is never going down regarding some desktop switches)
configure mac-locking ports port_list first-arrival aging enable
When enabled, first-arrival MAC addresses that are aged out of the forwarding database are removed from the associated port MAC lock. New MAC addresses can be learned until the configured first-arrival limit is reached.