Scaling / Number of simultanous connections

I'm about to start porting a Firebird DB to Postgres. Next thing will be upgrading all customers. Most of our customers have around 30 users or less. We have a few 'bigger' customers that maybe have 50 users or a bit more still. The application is a Delphi application that is in fact a 'fat' client that uses a permanent connection to the DB. I've read that Postgres uses 1 process per user. So that means 30-50 processes at the same time. 

I have 2 questions about this

- I guess this situation is not really a heavy workload? Or is it?

- And is it correct that a single process cannot access multiple CPU cores, so things are not multi threaded? I guess MySQL used that argument somewhere, but I'm not sure, forgive me if I'm mistaken.

The whole thing boils down to this question: Am I save with 30-50 simultanous users for speed and scaling?

Thanks a lot in advance!

Best regards, Nico