You don't need longer shocks with a body lift as everything the shocks attach to are part of the frame.

Do you already have the body lift? If not, I would do a suspension lift first. The suspension lift will improve your ride, handling, and ground clearance. The only real benefits to the body lift are a taller look and the ability to run 33 inch tires. The complication and difficulty of installation far outweigh the benefits. I would only do it as a last resort personally.

Yes, Bilsteins GOOD!