Consider adding the point of user to system resource ratio too.
Higher then number of simultaneous users and installed apps, more system resources you may need.
For example, my nextcloud installation runs fine with 2GB RAM and 512MB SWAP. Memory usage is around 1GB with no swapping in idle times, but when there is load of many concurrent users, system usage shoots up dramatically !!
At peak time, I have to allocate upto 16GB RAM to sustain the load for a responsive performance !!
Otherwise, this NextCloud VM (snap installation) is happy to cruise with 2GB RAM !!
Thanks.