Many community users have smaller setups, so usage statistics are then heavily depend on the use case, e.g. few sync mainly some contacts while other work on rather large files that are constantly synced.
User with larger setups don’t share much details. With the desktop client, you can probably make a few tests and estimate a load, especially the new high performance backend (also some numbers are in the announcement itself: Nextcloud faster than ever! Introducing Files High Performance Back-end).
there was a limit in the free version that only 10 people can use it at the same time.
You need that? If yes, I’d rather put it on the large server and use it in one virtual machine…
If you want to have video meeting via Talk, I’d test a bit the bandwidth used.
For Nextcloud, there is the federated share as well, so you can link between them, so if you require a lot of bandwidth for conferencing and also sharing documents externally, you could put this on a separate server with high bandwidth and use the in-house solution just for documents you are currently work on and share with other staff. So the load created by external download and conferences doesn’t bother you.