I'm glad you've made progress and are able to run now!
Strictly speaking, a 3D airport is not required for VR, it's just that PhotoFields are not able to provide the full benefits of VR due to their two-dimensional nature. So, 3D airports are recommended for the best experience, but you can still load PhotoFields in VR if you want. They do still work.
As far as launching RealFlight in VR mode, assuming everything is set up correctly on the Oculus side of things, it should simply be a matter of selecting the correct launch option for your VR setup after you have clicked the Play button in Steam. If you're selecting the same option each time but getting inconsistent results, that is confusing and incorrect behavior. It is worth pointing out that Steam gives you the option to say "Use this launch option every time and stop asking me". If you happen to have done that, it's probably best to undo it since it sounds like you do in fact want to run in different modes at different times. If you need help with that just ask; it's easy to change.
Re: controller setup, for your DX8 you should be able to just select the "Spektrum Receiver (7+ ch)" radio profile from the dropdown list in the controller menu and be done as far as RealFlight is concerned. It is already configured for you to support that radio. You may need to do some work on your TX though to set up a basic model in memory if you haven't already done so.