Good to see that you joined in on the fun, Chupito. As others said, always cool to see humans' collections, and hopefully your linen backed pieces will turn out well. If you have any questions about framing, I'm sure someone can help you, although it sounds like you have it all figured out, except the "juxtaposition."
What to use to hold down posters for photographing varies. I just use XBOX 360 game cases, some use paper weights that are glass, drinking glasses, or a board with magnets, whatever works best for you.