"Look under the bonnet of your car, remove everything and put back a single computer to control a single electric motor, and perhaps some aircon rads and a fan. Of course brakes and steering are still required"
You've left in the entire transmission. You might want to take that out and replace it with a motor at each wheel. You also have to think about regenerative breaking and how to recover power back into the battery, otherwise you're going to have a very short-range car. The aircon rads aren't going to be much use because you've removed the aircon pump which is driven by the engine.