When in doubt, run all the tires at max pressure.
Soft rear springs can cause alot of rocking, sagging, swaying issues. Most motorhomes are overloaded and need stiffer rear springs, especially those chassis which have alot of rear overhang length.
You can get a set of heavy duty leaf packs from SD Truck Springs or Stengel Bros.
Yes, heavy sway bars front and rear, with polyurethane bushings, will certainly help.
First ensure that your steering box, tie rod ends, ball joints and axle pivot bushings are all good. If any of those are bad, it doesn't matter what aftermarket stuff you add, it will still have poor steering and handling.
On the alignment, lots of toe-in and caster are a good thing.
