Really anything will do. The reply above mine is extreme overkill for Essentials, though it would be good if you're planning to do things other than Essentials I guess. But really, anything semi-recent will do the trick just fine. It's all just silly little sprite based RPGs made in a 20 year old game engine, so it doesn't take much at all to get them running. But if you want more specific recommendations, I'd say at least an intel i5 processor (more recent i3s might also work now that Essentials has updated to run better but it used to be hit or miss back when I had one), 8GB RAM but I doubt you'll find anything lower than that, there's no Essentials game that's gonna need more than 2GB at most anyway, and for graphics card really anything would work I guess, but if you want to do more gaming than just Essentials or other RMXP stuff, look into getting at least a GTX 1050 (or whatever AMD's equivalent would be)