[agiacalone]

> I found that 16GB on my laptop provided only enough memory for two app VMs

That seems...not right. I typically have 8-10 app Qubes running and don't have a problem, although I only use web browsers in a couple at a time, truth be told, which are my typical RAM use offenders.

Qubes, like most *nixes, will allocate all available RAM when it's free, so maybe that is where you are seeing the problem? When you run additional Qubes, the OS should balance and re-distribute RAM so it isn't typically an issue. I find that it works quite well for my uses.