Hey man... welcome, and congrats on the armor order! So glad you did research and didn't click that first button!
To answer your questions... #1, someone else can answer that... #2, do you mean the "side rivets?" If so, they're actually brads if you want to look accurate.... and #3, foam, all the way. No hard hat liners for me. I like the comfort and simplicity of foam!
Hope that helps, and can't wait to see the build threads!!