This is confusing and as you are a beginner, I'm thinking you may not understand all the licensing requirements or the technical requirements. It's important to realize that these are different things.
1) You need to know how to get things setup and running (technical)
2) You need to license everything properly (legal / licensing)
For the licensing part of it:
You need a Server CAL for every user / device that will access the Server. You mentioned 50 users above - is that how many you have? If so, you need 50 User CALs.
For RDS / Terminal Server access you need an RDS CAL for every user that will access for the Server for non admin work. You said you have 3 users that will be doing this? You need 3 RDS CALs.
Does that make sense?
