I'd definitely suggest renting a car is the best option to see Scotland. As far as where you pick it up from, Edinburgh's city centre (okay... center) is a little bit fiddly so if you're going to take that option then AVOID RUSH HOUR LIKE THE PLAGUE. Otherwise - it shouldn't be that tough. Don't worry about the speed cameras - just don't speed!

I'm assuming it's no more difficult for an American to drive on the left hand side of the road than it is for me to drive on the right hand side. However - make sure you know how to navigate a roundabout as these apparently cause problems.

Also - make sure you are either happy driving a manual (okay... stick shift) or specify an automatic when you order the car.

It might be wroth giving Arnold Clark a try. They are big and reputable and I would have thought they'd have to undercut the majors given that they are only in the UK although I haven't compared prices.