If you are going to be working in UE4 seriously, I’d recommend putting UE4 and any incorporated/used software (Visual Studio, etc.) on an SSD. I have a 500Gb SSD for my OS and software, and then a seperate 500Gb SSD for the project themselves (I just relocated my Documents folder to my other SSD). With a few engine versions, and the engine compiled from source, I am using up about 150Gb in engine installations alone. As far as your projects go, things like autosaves and such can add up to a lot of space, fairly quickly. If you are like me and don’t like having to delete those sorts of things, I would recommend reserving a good chunk of space (100Gb+ for a modest user) for projects, wherever you may store them.