I have been patiently waiting for years for the GFX to dip into the sub-$2000 range and I finally picked up a 50R. Very excited! I know it's not the latest, but I do still portraits, and have my Z for anything fast-moving.
In my D850 days I loved my ART 50. I'm happiest doing environmental portraits shots, sometimes wide-open without OCF (Octa) or stopped-down with flash. That said, what would people recommend, adapted or native for a 45-50mm-ish FoV for portraits? The Fuji 63? The body I got will come with the Mitakon 65, but it made be hard for me to do MF -- we shall see.
I might be the outlier here, but I think the 32-64 is the most versatile portrait lens in the lineup. At 64mm and f/4, the lens has a wonderful quality to the falloff and bokeh. And since the CDAF of the 50R isn't the best AF for things in motion, f/4 gives more keepers.
For primes, if you prefer the 50mm FOV on full frame, I recommend the GF 50. The GF 50 has much faster AF than the GF 63, and this is especially important when using the 50R (CDAF) versus the 100S (PDAF). Think of the GF 50 as the same 50mm lens you've been using on full frame, but your subject extended their arms and pushed out the borders of the image a bit on the sides and more on the top and bottom – and that is the image you get with the GF 50 on our 50R. I know the GF 63 is the technical equivalent to 50mm on full frame, but focal length is focal length, and I've found that if I like a given focal length, I prefer to stick with it even on a larger sensor. YMMV of course, just something to consider.
Also re: your Mitakon 65 – the look of that wide open on your 50R will be unreal, and you might become addicted to that look. You can go with the GF 80 or 110, but there is something unique about a very wide aperture with a wider FOV that I find unique. Fujfilm has a GF 55 1.7 in the works, so if you like the Mitakon, that might be the lens to save up for when it eventually is released.