So if you buy something from the oculus store then you dont also get the steam version, and vice versa if you buy from Steam you dont get it on oculus store?
Yes
For a cross buy title do you buy it on quest or oculus store first?
Cross buy titles are on the Oculus Store on your PC and not in the Quest section. Look up a game and check in the description it includes Quest as compatible if it is a cross buy. So you can then play the native Quest version.
If its not listing Quest in the compatible part in the description you can still buy it but will need to use link or VD to play it.
All games bought via the actual Quest are native Quest games.
And can the oculus store (rift) titles be played via the virtual desktop wireless option or only via oculus link?
Can be played via link or VD. Asking this question makes me think you dont quite understand what playing from your PC is.
Imagine your Quest being a monitor. Your PC is playing the game and outputting the display via link or wifi (Virtual Desktop) to your Quest. All you are using your Quest for is the display, sound and the controller.
What connection speeds are you all getting using virtual desktop?
Ive set all the options to high and the VD settings screen shows im connected to the 5ghz wifi at 400 Mbps and then at the bottom right of the screen its saying my bitrate is 30.9 Mbps. Ive read it should be far higher than this?
My minimum is around 500Mbps on WIFI 5ghz - 30.9Mbps is more than fine I dont know where you have read this but its rubbish. The higher the better yes but that is fine.
Picture Quality - Netflix is (or was) around 15Mbps, Bluray is 25Mbps+ so 30.9Mbps is better than Bluray quality (approximation)
30.9Mbps you should be able to set your setting to Ultra as mine is slightly lower than yours and I have it on Ultra fine. What is just as important is latency and it tells you this on the left. Mine was 20ms last time I looked. If you think about your monitor you might have one that is 1ms or 5ms. TV's are or were around 20ms-25ms (if IIRC) (not all TV's) so you ideally need to be around this or less.
I think you need to do less thinking about it and more playing !
I have tinkered with my VD settings so I will let you know what mine are when I fire it up not used Quest for a while but I have tinkered with some of the other settings to get better performance.