Well I've started the process. Scored a good deal on an Intel 512Gb 600p SSD, and just ordered a Fractal Design Meshify C case along with a Corsair 650W PSU.

I've decided to pass on a second SSD for games for now, save for a 1-2 TB one down the track (that Crucial MX300 2tb looks nice and affordable) and just use one of my 1Tb HDDs for games storage. Any brand new must play asap games I can install on the SSD and then move the files over later (Steam's good for this, as are some of the other launcher platforms.)

Still haven't 100% decided which way to go, but I'm edging towards a Ryzen 1700/X370 combo, as I've decided to keep my old Mac Pro and roll it back to a fresh OS X 10.6.8 install, so I've got no compatibility issues with any of my music software, powercore card, audio interface(s) etc, and have it as a dedicated music box, and a backup system if the new comp goes down.
Won't even need a KVM switch as the monitor has multiple inputs, and my Apple keyboard is on an extension cable, all I have to do is just unplug it from one extension, and plug it into the next (I already have a spare.) Will probably plug the mouse into the keyboard and cable tie part of the cable to the keyboard so it's less messy on the desk.