I can describe my experience with menus like station board & galactic map. When I land at a station and launch station services, I do see some brief glitching while the menu loads. After that, it runs mostly fine, either using the mouse or the HOTAS. Switching between submenus, like commodities and mission board may or may not produce a brief glitch. Overall, it's not affecting the game, even if I'd prefer things to be smoother.
The galactic map is another problem. Loading it again causes some glitching, but the map itself is fine. However, trying to select stars is very buggy. The mouse cursor floats there and is not aligned to anything in particular. That makes things somewhat difficult :/
While playing, I do see judder, dropped frame, etc. I see some, but my system is not top notch (1060GTX/i5 3570) and my headset is 1440x1440, higher resolution than a rift or a vive... It happens mostly when the game loads something: checking a new body, ship. Overall, I think ED is very poorly optimized. Planets and stars look like they're taxing the system, making the frame rate drop. Big, poorly textured spheres are too hard to render? Seriously?
As for your other problems:
1- there's some flaring. I can see it most when the ship is sitting in the hangar with bright ceiling lights. It's annoying, but not game-breaking to me.
2-my HMD fits okay, certainly not too tight
As an aside, why are you hell bent on replacing your Rift with a WMR? Is there something wrong with it?