Concurrent connections supported

You will need to have two users log into the server and observe the memory and cpu requirements for those two users actively using the POS sale application and then extrapolate from there.

What is the disk subsystem the server is using, a multi disk RAID 10 or RAID 5 system with maybe 5 or 6  disks (not including parity or hotspares) should be sufficient but it largely depends on the number of users actively using it as a file server as well.

Are we looking at tens or hundreds of users, is the server connected via gigabit ethernet, lots of large files or many small ones, mainly reads or writes or a even mixture?

To be perfectly honest the hardware you've given us so far sounds underpowered for what you are intending, any upgrade options available?

Thank you. Can you comment on possible requirements after you view the attached pic showing connected users & Task Manager?

Looking at the memory usage I'd suggest 18 to 20 users maximum, I've no idea from that screenshot how your disk system is coping, you can monitor the disks queues in Performance Monitoring to see how they are, the queues should be very low on a system that that is keeping up with the reads and writes but to be honest you could probably tell from the performance of your apps in the sessions whether you are having problems or not.

I would however suggest putting more RAM in the server, the more the better.

How many users do you want to get connected to the server?

I want to connect another 35 users. See pic of perf counter