I just went through the same process on a used Rockwood. You want the tongue weight rating of the hitch to be close to the tongue weight of your rig. It should slightly higher than the actual tongue weight and within around 250 pounds. Then it will be strong enough but not have a harsh ride. It sounds like your old hitch would work fine.
Ideally your hitch ball height will be about an inch to an inch and a half higher than your level trailer hitch at rest. Then when you place the tongue weight on the truck and add the WE hitch you will be close to level. I set up my outfit and compared the fender well heights on my truck to the undladen heights. The front was actually 1/2 in lower, so I added another link and now it is level.
