If you are going to do major suspension changes that include brake system changes, go through the brake system (hoses, standard-metal lines, wheel cylinders, master cylinder, and shoes/hardware. No need for SS lines and converting to dual master cylinder now if you might change your brake system substantially in the near future (and might end up with disc brakes).
Depending on what you plan for the future (and how soon), I'd next go into replacing worn parts in the front-end and steering parts (they are not expensive, they are easy to work on, and a tight front-end allows these trucks to drive remarkably straight and smooth).
