We often have people ask whether they can use a Mac mini, and also run Parallels so they can run a Windows Server. So far, doing this has been no problem for the Mac minis. You can run a version of Windows Server and use those services.
From our experience, the 4GB is more than enough for this. But, if you really want to make sure both OS’s have plenty of RAM, then the 8GB or 16GB has worked real well.