It depends a bit on how much data the pool is making you upload, and other minor factor, but a hundred devices would probably still be in low mid 2 digits kbps. If that become a problem, you can use a local proxy, but it's in most case, not a problem. The bottleneck is usually active connections handled by consumer grade routers. For example i have one device atm using an average of 0.4kbps with U/D combined.

If you have money for a massive farm, you can probably afford a 70$ router using custom firmware or a used industrial grade one.