Usually the FOV is set between 70 and 85 for regular FPS gameplay, but for cinematic effects or close up face shots even an FOV of 30 can be desired. What I mean is the desired FOV is not directly related to the screen width. However, some FOV values which are too big can cause warping on screens which are not wide.
I have not tried a very wide screen myself but, don’t high values of FOV only make sense on curved screens?
You can set the FOV from a PlayerCameraManager, accessible from any PlayerController.
You can the viewport size from APlayerController::GetViewportSize().