My advice, such as it is, is perhaps build a quick and dirty test piece and try everything on that. If it works, proceed with the model; if not, you haven't just wasted your entire model, just a small test part.
#1 - no clue, as I haven't used it myself and am actually awaiting your results so I know how to proceed
#2 - that's how I read it
#3 - filled & smooth is filled & smooth. If a couple of coats of this does the job, then great. Proceed in the next step of finishing.
#4 - build & cover a test piece and see what happens
Steve
ps - the offer still stands if someone wants to split one of those cases of the doc paper silkspan (light and/or medium).