adding a leaf springs?

Adding a leaf ot two will not noticeably lift a truck. All you'll do is increase spring rate. Companies make re-arched spring stacks. The economical way is to build a spacer between the main leaf and the differential spring saddle. Your spring rate won't change. It won't ride like a brick. You'll need to toss in a longer set of U bolts on each side.

Any time you lift the rear suspension only you loose positive caster. No sweat if you have a double wishbone front suspension as it can be corrected.

use the same ones, adding leaf springs just changes the amount of weight the suspension can handle. you can change the leaf spring supports to longer ones to add a little lift.

Use the same ones. You only want to add a leaf if you're going to be hauling heavier loads; not to just lift the truck.

You would need more if you had + 8 kids and w/Kate too

same ones.