Jeff,
congratulations on starting your TX. There's something cool about black armor. As far as undersuit, UnderArmour works great, but a lot of us save money by buying compression gear from Eastbay.com. Shoulder pauldrons are usually pretty easy to score unless you have a larger neck. I think shoulderpauldrons.com still sells them; Trooperbay.com as well. Trooper1 over at the MEPD has the best ones, but he is pricey. Neck seals: Darman, Ladysewsforus, and TK409 make them. You can get them with velcro or zipper closures in the back. I have velcro on mine because I lack confidence that I can zip behind my neck by myself. Others may have a different opinion on that. Darman over at whitearmor.net is the most affordable and fastest to ship usually. I hope that helps. Please continue to ask questions and godspeed on your build.