start by asking your colleagues what they use
It's both fun and nerve-wracking when you have to decide how to set up your new lab. You want to make sure that you do everything right at the start so that you hopefully can do your research without any problems down the road. If you are going to use the latest version of DirectRT and/or Medialab, you should be free to choose most any hardware and OS you want.
That being said, I would suggest you see if any colleagues in your institution also use DirectRT. They will have insight into if any issues occurred because of contextual factors that would occur outside of your lab. For example, if you are going to use DirectRT through a site license, what computers are fairly "standard" at your institution? How does any IT service work for issues that may arise like malfunctions or license renewal/expansion? Were there any past issues with particular machines so that you can avoid that hardware? Hopefully this will help you figure out how to make choices informed by what worked and didn't for others in your new workplace.