Air ride is the thing I know the best. Ok before I answer the valve sizing question I need to know what are your intentions with it? Do you want to be able to park and air it out and that be it, or do you want to be able to sit there and play with the switches at a light to get the cute girls attention next to you? Also do you want front and back or do you want front back side to side?

As far as where to put the valves it doesnt really make that noticeable of a difference so put the valves somewhere where you want them. With the speed of the setup air pressure is more important than location.

Plumbing them is something that can be tricky because theyre so many ways to do it. Once you figure out where your tank and valves are going to go I can help you figure it out. One thing I do recommend is to go with all PTC (push to connect) fittings. They make life a lot simpler because you dont have to worry about as much air possibly leaking out when you are putting it all together.