It all depends on:
- your CPU and memory
- features configured on routers (especially IPSec)
- traffic flow on links between routers
And regarding your question: yes, running 100 routers is possible:https://www.youtube.com/watch?v=_NGLsh0KDDk
But having 100 routers without any link (IMO) makes no sense :)
Using 20 routers connected and makinkg some important things makes far more sense (for me).
And with even 10 routers you can make quite complex topology and test something more valuable than your CPU power :)