An update.
After much on-line research, which was thoroughly enjoyable, I have decided to go with a pre-built small form build:
i5 11600K
ASUS ROG STRIX Z590-l Gaming WiFi
32Gb Corsair Vengeance DDR4 3600 Mhz
RTX 3060 TI 8Gb
Corsair 650W Gold PSU
2 Tb PCIe M2 - this should be plenty as FS2020 add-on storage demands are relatively small to P3D etc I have found.
My options were limited in some areas [mobo/gpu] as you can imagine, but having seen some YouTube vids specifically for this CPU/GPU combo, I'm pretty confident this rig will give me good results - hopefully for years to come!!!
I could stretch to an i7 CPU, but is it required? I'm tempted, but if it's not going to do anything appreciable..........
So, comments are more than welcome.