Once the licensing grace period has passed, you must have a license for each connecting user or device to connect to an RD Session Host server. You'll also need to activate the RDS Licensing on the server.
You'll need to purchase RDS Client Access Licenses (CALs) and install them on the RDS Licensing Server. These RDS CALs will be tied to the server, but RDS lets you move them to new hardware when needed. Remember that RDS supports both per-user and per-device licensing. The model you choose should depend on whether you have more users or computers. RDS does not have concurrent-user licensing, and the licenses you select must match the mode for which you configure the RD Session Host server.
You can virtualize an RD Session Host server, but you'll likely see a reduction in the number of simultaneous sessions it can support. Be sure to model on the same machine type (physical or virtual) you intend to use. If you do build a virtual RD Session Host server, you should probably use a server with a processor supporting second-level address translation (SLAT) to reduce the overhead of memory mapping between the physical machine and the VMs. To minimize cost, its also advisable to use a Type 1 hypervisor like Hyper-V, not a Type 2.