Hi
Very easy to answer the question about the FOV: You can't
The 140/120/90 are not changing the the FOV but are just cropping.
Best way to avoid the curved/fish eye effect is to shoot straight on. As soon as you turn the camera up and down you get the Fish eye effect. Try to take a Video, just hovering, start pointing the the Camera all the down and the slowly go all the way up with the camera. When you are watching the video after you are able to see how the fish eye effect nearly disappear when the the camera is horizontal.
But of course you cant use it like that, so the next way are to use the Lens profile from Adobe/DJI which can be used in both Photoshop and Adobe Light Room.
Hope that makes sense?