I don't have any specific suggestions as I don't have a Nineteen. But your post is interesting because yours is the first case I've heard of the short sprinter receiving anything but praise.
But as a general rule, always start with shocks. I went with Koni's on my '2012 Chevy Express-based Avenue Suite (nearly identical floorplan to the Nineteen). Koni's are really expensive and are not gas-charged, which was the reason I wanted them over other shocks as I believe it makes them more compliant on initial road impacts. They are excellent at controlling secondary motions even though out of the box they appeared to offer little compression resistance (could be compressed by hand).
After installing the Koni FSD's, I never considered needing any other suspension changes.