This varies widely depending on the application. A properly configured RD&T box on good sized hardware can support many users and may be a good candidate for integrated testing scenarios before system test. Smaller boxes configured for unit test use may work perfectly well for one or two users. An alternate question might be how do you intend to create your master image for RD&T and how and where will you deploy it. This is probably going to a better determiner of what size box you use and how many users you assign to it.
RDz-UT and RD&T run only on Intel Linux. They do not run on Linux on System z.
RDzJohn
RDzJohn