Not sure of the size difference with 403a, I sold a bunch of those to Japan...

I tie pars together with nylon ties. A pair can fit a large flat rate USPS box.

I prefer 1/8 inch foam in multiple layers...not foam rubber but the white plastic kind.

Prices can vary. I would do auctions starting at 250 for 7 days. Offering to ship east as in the Orient helps.

As has been mentioned you can post in the classifieds here free and reach users, but users tend not to be as rich as collectors. You have enough to do both.