Several vpn servers with one client

Hello!

I have one Mikrotik router, it works like our vpn (ppp) server, have seperate radius server on centos, but in future im going to add more mikrotik routers as vpn servers, its because vpn clients number is growing, and i dont know exactly how much vpn connections is crictical for one mikrotik router. And im wondering is it possible to divide traffic somehow if i add an extra mikrotik routers, do i need to seperate ip pools one each router for clients, or they must be the same, or simply point me where to start?
Situation is like that we have our software, our vpn client and there is a built in one vpn server address, maybe someone has solution if clients connects to built in address (mikrotik vpn server) from software and after that mikrotik redirects client to one of the other mikrotik routers which is not on load (not so many clients connected). Or how to better do that? The right way?
Thank you in advance!