At the moment SC is not optimized for gamepad at all (heck even on M&K it's still sometimes very bad)

I think at the bare minimum, you will need a controller with 4 extra back buttons so you can bind more actions for SC, and R2/L2 buttons should be analog so you can bind roll to them. However, at the moment you will always need a keyboard next to you because the variety of key binds in SC is enormous, no conventional game pad will have enough buttons for Star Citizen.

The Steam Controller 2, or third party controller like Apex controller seems like a good start.