Step 1: I would fit the outer floor extension/inner rocker piece. The inner rocker in Your IMGUR album is junk. It Does not have any material behind the pillars or the proper contour. That is more of a patch for those who do not need total pillar replacement.
Step 2: fit and install the inner kick panel. As you can see it only covers the top two holes of the cab support therefore the tapered gap you have is necessary.
Step 3: fit and install the pillar. Once you get to this point the gap should be minimal.
Step 4: hang the door, remove striker plate for cab jamb.
Step 5: begin fitting the outer rocker.
You honestly have a huge job ahead of you. You could save a lot of time and frustration by purchasing a complete cab floor. I know from experience.
