This kind of server is for the moment rare in the free software world. It's more frequent in Microsoft world, by association with
Metaframe solutions of Citrix.
An office server needs 50 MB of RAM per user.
Intrinsically, this machine has no requirements in term of disk, if it's not at the same time a file server.
Processor resources used are important, thus it could be useful to consider the increase in frequency and the addition of processors, because this type of traffic could be quite well done in parallel.