Quest 2 is definitely a good choice for dipping your toes into VR, but do bear in mind that at first MSFS is expected to be exclusive to WMR for an unknown period of time and support for other headsets is supposed to come later. We don’t yet know when.
Unfortunately all VR beta testers are also still under nda so we have no idea at all exactly how the VR in MSFS2020 runs yet.
Given the flat game however, we can probably guess it’ll be extremely demanding to run at high settings... so the simple answer is the most powerful GPU you can afford, as it still won’t be enough!
The game is also, as it currently stands at least, very demanding on single threaded CPU performance and easily becomes main thread bottlenecked. They are aiming to improve this as time goes on but that’s where we currently are - so give thought to what CPU you are using too.
I think it is likely that most will end up trying to get the game to run at 45fps and then using reprojection.
EDIT - just to update this, we found out recently that VR is scheduled for the 23rd December and contrary to what they originally said it'll be coming too all headsets at the same time.