My numbers are closely matching (maybe 1-2psi off tops). As you probably know, check PSI with cold tires that haven’t been driven on and average ambient temperature.
Reese make some WDH… hopefully the RV dealer can advise you of the proper model. As you probably know, the WDH will keep the rig level and increase stability.
Long wheelbases tend to tow better. Make sure you have a sway control device. It doesn’t take long to get a few thousand pounds of stuff in an RV… fresh water tank, supplies etc. Personally I wouldn’t exceed 5k total weight which sounds realistic if you pack conservatively. Enjoy !
Just keep in mind that 4500 is the dry weight. With equipment and everything you will probably get closer to the 7500 pound max the truck can tow. If you plan on doing trips at high elevations that could get marginal. Made sure your running premium fuel when towing for optimal performance.