I have an '05 F150 Scab HD 4x4 package, so they are definately available. Most dealers are clueless about these trucks, so it may take some diligence on your part to get someone who knows about them.
The whole rear suspension, driveshaft, differential (4.10) are different from regular F150's, so I'm not sure if the leafs are interchangeable. I can take measurements of mine if that helps.
The truck is not "stiff" like an F250 or 350 (I've owned both of those) and rides exceptionally smooth and quiet. It can easily carry a ton. This is the reason I bought it instead of a F350 diesel.
As far as wheels, they are 7 lug but that doesn't bother me. Check on ebay they are made by Eagle wheels. They are starting to become available and I would never buy a vehicle based on wheel selection.