Brake mixing: ESC plugged into throttle channel, brake servo plugged into aux channel. You use mixing in the radio so both channels operate from throttle input (trigger).
get busy with your conversion and run the clutch, being able to set your braking bias is a great feature you will lose if you go direct drive.
As for your controller keep it and use a y connector, if you like it and want to neaten up your set up (and make it more tuneable) then upgrade your radio
Enjoy these are great kits