TSplus can handle up to 50-60 users on a single standard server.
Some of our clients, using over the top servers, can handle around 100 users at once. 

This really depends on the server's hardware and what applications you published for your users.

However, for over 50 concurrent sessions, we recommend to use a farm of servers. 

Each server (physical or virtual ones) handling up to 50 concurrent users.

The type of hardware you need will mostly depend on what kind of resources the applications you wish to publish . 

You might consider getting a server with SSD drives if you plan on using an application that accesses a database on your TSplus server as it will greatly enhance the performances.

For a better understanding, please check our documentation here: TSplus prerequisites