Wow, I've had my NX4510HST Cab a year now, with 75+ hrs, and the only issue I've had that you list is the occasional need to bump the HST pedals forward or reverse to change ranges. That can be an irritation, but I just nurse is for a few seconds when that happens, and I don't shift between ranges very often. Goes to show YMMV.
My QH is a 10 or 12 y/o Harbor Freight Cat 1, and doesn't cause any clearance problem with the rear fenders so long as the release levers are not left in the up position when there's no implement and the hitch is fully raised. From Eric's reports, sounds like it's different with a Cat 2 QH, as they are a bit wider. Even with a Cat 1, though, you do have to be careful to stay clear of the QH when raising and lowering from behind the tractor using the remote hydraulic lever. Otherwise you can get pinched between the corner of the QH and the fender.
Instead of the factory radio, I put in an inexpensive aftermarket with AM/FM and weatherband. Works fine for me, but I'm no audiophile, especially when on the tractor. I can see how it would be tough to do a flush mount with larger speakers.
No problems at all so far with dust infiltration into the closed cab. No problems with FEL hydraulic hoses rubbing.
Re your pt. 2, I don't have a clearance issue with the arm rest, with the seat fully back, where I prefer it. Not sure what you mean by cheap plastic; you may have higher standards than I for tractor cab interiors.

Compared to the 2014 Kubota
L4760 (Grand L), which I was ready to buy until I looked at the NX4510, I didn't see much difference. My wife helped me a bit with the shopping, and I was quite surprised when she got into the Kioti and said she thought the interior was actually nicer. :confused3:
Your point 4, when you move into a pile with anti-stall activated, are you stalling out even in low and medium range? FWIW, even though I run in Linked Pedal mode most of the time, I still throttle up manually to full PTO speed when doing loader work.