I’m pretty happy with my 2700X.
I do think you may be able to build two AM4 based machines to split the work between them cheaper than one threadripper that is big enough spec to do it all at the same time. It will run close, definitely.
I personally don’t like the idea of NAS in my main machine, i’d go all SSD in the workstation/gaming box (they’re cheap enough now) and split the noisy/slow spinny disks off to a dedicated NAS box (something like a B350 based ryzen 2200G or previous gen baseline R3 or such) that you can put out of the way / further away from your ears, etc.
Keeping your NAS seperate will also reduce risk, etc. of your gaming activities impacting your NAS (crash due to game/video driver/malware/whatever, reboot required for updates, etc.). To be clear i’d run Windows on bare metal on the 2700X gaming box and FreeNAS on the B350 based NAS. I’d run plex via freeNAS plugin. I’d do VMs with either HyperV or VMWare Workstation (or virtualbox if so inclined). If you need to game in a room other than where the PCs is, do via steam link box (or steam running over the network, streaming - so long as you don’t need to game in both places at same time).
One big threadripper system will be a compromise IMHO (mostly because of the NAS concerns above), and i don’t think you’ll save much by trying to cram everything into one machine. TR board plus bigger PSU plus TR CPU = almost/likely able to buy a B350 board and second smaller PSU, with the cost difference. I dunno if you’d be able to get a case as well, but you could also drop to a b350/b450 board on your 2700x as well to shave costs. You could also maybe drop to a 2600X to further shave costs… if you had to.
You’d need to buy enough RAM to do it all whether it is all in one TR box or split between two Ryzen boxes.
A single TR box will be less flexible too IMHO. The 2700X will be better at gaming as well (if that’s a concern).
Trying to make one box do it all via virtualised windows gaming VMs might be funky and interesting, but it will not work as well as a dedicated gaming PC. And you WILL spend a lot of time setting it all up and dealing with any wierd issues that you might seen in games, etc.