SIG7Pro
I hate my life.
I'd say, for me, I use the default layouts, except I remap spin to right shift, remap Custom 1, 2, and 3 to 8, 9, and 0, and if I were to be playing on Windows, I would remap spectate to R, despite the game lagging heavily if I were to join online games on Windows (I have a bad laptop.)
For Kart, I kind of got used to the controls that I haven't changed it.
I also play in Standard mode or Legacy/Strafe mode, but the simple mode (or whatever its called) is also good, thats what i mainly got used to as well back when i played it on mobile and web.