With regards to PC > Quest 2 it all depends on the connection. If you are using a USB C 3.1 cable and connecting via Oculus link this will often give you the best visual experience.
Read this for more info
https://uploadvr.com/oculus-link-resolution-increase-odt/
If you are going to use Airlink, the wireless version of Oculus Link this will not give you the best visual quality as it depends on things like your WIFI connection but again the settings can be changed with the Oculus Debug Tool in the above link. Have a look at this link also >
https://forums.overclockers.co.uk/threads/quest-2-which-wifi6-router.18900781/
Virtual Desktop is the third popular choice and this is available via the Oculus store for about £9 (the two above are free) and is arguably the best solution for Quest2 Wireless play via a PC. The quality can be better than Airlink and the quality is nearly as good as using an USB cable, dependant on WIFI connection being excellent too.
No. Whichever method you use above you need to adjust the settings yourself.
This is not as straightforward. The Quest 2 can now support 120hz, SteamVR on mine reports 120hz but it can be dependant on the game. Virtual Desktop does 90hz and some games support 120hz.
Yes you can but what you have to remember is there are the graphics settings for the game, and there are also quality settings for the "stream" to the Quest 2.
With PC > Quest2 what it basically does is use the Quest2 as "monitors" to display a stream from the PC (like Geforce Now does) so it all depends on the quality of the stream being sent to the Quest 2 and this can be adjusted manually.
On another note native Quest 2 games will always give you the best visual quality but remember native games run on the native Quest 2 hardware so its basically liked a suped up mobile phone with bells on so the visual quality of the graphics/textures etc will never be as good as a PC > Quest 2 version. After the Fall and Resident Evil native come very close on the Quest 2.
