You have a classic there.
I recently restored one to running condition. It was a light restoration - I didn't clean the 'patina' off the body, but the chassis had a good scrub and clean. My biggest problem was a broken gear tooth, it took a while to source a replacement but I finally got one after lurking on Ebay for acouple of months.
I bought new tires - they are the Rough Rider ones for the rear but orginal Sand Rover for the fronts. The old tires were hard and crumbly.
I'm using the orginal speed controller (mechanical) and a 7.2V hump-pack which I found on Ebay.
The front suspension mounts were cracked and broken, so I made new mounts out of aluminium plate.
The last thing I replaced was the front bumper - I foolishly lifted the car by the front bumper and the orignal one just snapped! Fortunately I was able to get a new bumper to replace it.
Whateverr you do, a car of this age will never stand the abuse of a modern car. Have fun restoring it and drive it gently!
See my restoration progress at: