I would swap the Central & Proxy node based on your configuration. There's no need to have 16GB on a proxy node and on the other hand the central node might need it, especially as it's going to perform reloads.
What app sizes do you expect to have, and reload frequency? To me the 2 CPU cores seem far too little for 100+ users.
Thanks Martin. I can ask that the memory amount for the 2 servers to be swapped. I will also try to get the CPUs upgraded to 4 cores on all 4 servers, do you think that's enough? Which of the services is most CPU intensive?
What do you think about the overall architecture? Would you do it differently?
Also, what do you think about the Scheduler? Is it OK on Central Node + the 2 Engine nodes?
Honestly I have no idea on the App size. In the POC installation that they used so far, the largest app size was quite small - 140 MB excluding the Operations Monitor app.