My opinion is the total number of users is irrelevant. It is important to how many simultaneous connections PPOoE you can give on your IP subnet.
This determines the load on the server.
i changed the maximum users of PPPOE server from config.xml to 50000 number .
but the problem is that the pfsence menu and web interface is loading very very slow.
i see the interfaces added.
13000 interfaces added with name of poes10(0) ~ poes12600(0) to my interface assign list