As wild said, for ground vehicles a mouse and keyboard is fine. They control exactly the same as they do in RB but your view is limited to the commanders position and your gunsight position now affects where your shell hits. (In RB your gun sight is straight down the middle of the barrel)

As for aircraft. For a reasonable experience you need a joystick and some form of head-tracking. I wouldn't recommend VR if you want to actually play as VR is more of a gimmick in War Thunder rather than a useful tool.

In terms of joysticks. A firm favourite on the lower-end of the price range is the Logitech Extreme 3D pro. It's an older design so you can get a new one for around £30 (40$).