Yes, you should paint the brackets white.
You may need to heat bend the butt plate a little so it doesn't flare out the sides. Your shim looks good, just keep in mind that ideally the top of the kidney lines up with the top of the ab plate.
Yes, I would heat bend (using a hot water bath) the kidney and butt plate inwards a bit. There are several options for joining the ab and kidney. I used a sort of tab system which lcoks the pieces together and keeps them aligned and prevent any overlap. Would also suggest that you may want to bend the but plate a bit where it goes between your legs as it's pointing down a lot on you.
You may have to go with the hero Luke look and cut some off the bottom of the chest plate.
Cricket did this here: https://www.whitearmor.net/forum/topic/45339-crickets-rs-props-hero-build-yet-more-vertically-challenged-assembly/
Looks like an easy pass for basic. Echoing the comment regarding the drop box strap length. Would also suggest you secure them to ensure they are correctly aligned with the ends of the ABS belt.
Match it up with the ab to ensure that's the correct orientation. Note that the notches are not required. If you don't have to cut them out, I wouldn't bother. Your call though!
Not sure that I fully get what happened here...looks like you need to shim the forearms but shimmed the side that has a ridge instead of the side that doesn't appear to have a ridge? I would put the shim on the latter. Won't be able to see the shim (depending on the size required) and the side with the ridge will then have a correct size cover strip. If I misunderstood and this would not resolve your situation, please feel free to clarify!