65 Barracuda Front end Rebuild several questions and a couple of observations

I have finally finished tearing apart the front end parts for my Cuda and turning the corner towards re-assembly! This has been a pretty big deal for me, but you guys are a big help. First off, someone recommended this kit to break apart the components.....



Amazon 45 bucks. I hate to think about undoing all that stuff with a pickle fork and hammer! This kit made everything come apart relatively easily. Second observation is that I sprung for a nice 1/2" cordless impact driver, which also seems to be worth its weight in gold.
Front end rebuild kit from PST (rubber), 10" drum brakes that I'm going to continue to use.
I have a milk crate filled with with the backing plates, upper A arms, lower control arms and spindles, ready to go to the machine shop to have the new bushings pushed in/out and sandblasted for painting.
Questions:

• de-greased and cleaned up the spindles, when I noticed a very thin film gasket of some sort, barely there, but do I need to replace it? What is it for and where can I buy such a weird thing? I also noticed that the spindle seems to be made out of a different metal that the other iron components in the front. Sort of a copper/brass colored material. Is it different, and does it need to be treated differently when it comes to re-painting?

• Backing plates....On the front side, there is a half circle sized dust shield, I suppose? It is totally missing on the other side. Doesn't look like it can be put back on...Is it necessary? Do I need to get a whole new backing plate just because of this? Also, you'll notice in the picture that there are 2 small oblong rubber plugs in one of the backing plates, again, missing in the other side. Where can I source those small parts?

• What front suspension parts can I paint? Which should I leave alone? What paint and finish?
• The inner fender wells are stark naked! I sprayed de-greaser up in there and pressure washed the whole area. It's nice and clean, ready to be put back together. There is a hard undercoating material that is chipped away all over. I want to clean that up. I have seen people use a thick brush applied undercoating material on YouTube. Is that what I need to do here? What kind of surface prep? What is the best choice of undercoating material? I assume I re-paint the other parts with a rattle can.

I'm sure I will have lots more questions as I go, but this is a start. Thanks in advance my FABO brothers!