Hi Mitch!
OK, first off...filling the seams....there are many methods of filling up those nasty seams, my friend, the choice really, is up to the size of the seam, and (as is in your case) accessability...putty, is the standard, and if you have the room to effectively work with this media, then that's what I would do...for small seams, I like to use super glue, the thin stuff, and rely on capilary action to carry the glue down the seam...a little at a time works best, building in layers as you go...it can be sanded smooth also, if you use a superfine grit paper. Mr. Surfacer is another choice for seams, that works well if available to you. Follow this link to learn more about it;
Mr. Surfacer As far as your question #2, gimme a little time to find a reference, mate, I'm at the office and my library's at home!
Question #3, my friend, PE...I personally add PE as the final touch, (unless an addition of a certain PE part is holding up the build) and such as guardrails, I put them up raw (unpainted) and then paint in place...
I'll see what I can find on the net about the hangerbay colors, mate, but someone else may help you before I find something for you...
~Gunny