Starting off, pre build?

I’ve been reading through the forum and a lot of posts say that that poster is a noob…well I’m the ultimate ha. I’m really wanting to move up from my Synology ds216j and Mac mini running Ubuntu server. I’m looking for a build that I can happily run 3 or 4 VMs, Plex server and a NAS, currently have 2 x 10tb hdd. I think I am better off starting with a pre built and slowly upgrading, I’ve looked at the Lenovo D30 and Dell T7610 but wondering if I am aiming higher than what I need?