Good, only one small mistake. You only leave a gap on the left hand side, the tension end. On the right you want the 12mm nut to grip the angular bearing inner ring against the step in the screw. That gives you something to tighten the nut against so it stays where you put it. Don't want that right end nut free to unscrew itself.

The gap on the left only needs to be long enough to stop the 16mm part of the screw ever touching the bearing. If it does touch then the Belleville washers stop pulling on the screw.

My handle fitted inside the saddle, if it didn't I would have extended it. My X motor didn't fit so I extended that end a long way.

The extension can be as long as you need, it doesn't have to be wide.
A wide extension could get in the way of the motor. Allow room for the motor, you don't want the motor hitting the saddle or getting in the way when you want to turn the handle.
The extension has to take a big axial load from the Bellevilles.
The radial load is the motor torque.
The side loading is ordinary workshop bumps and knocks.
It has to hold the bearing square, otherwise the screw will flex when you turn it.
It is comforting if the extension carries any motor heat in to the bed, so the screw doesn't warm up.