Looking for some advice for our steep driveway

If your brakes are properly adjusted and you adjust the brake controller to the max you won't have a problem.

WD should be hooked up, if you don't use it the steering is going to be on the light side.

You've got a very good buddy if he's going to let you tether to his truck, I hope it's a dump truck. You certainly shouldn't keep any slack in the line, if something where to happen the initial pull on the chain would probably over come any positive effects that the tether would have.