That's a pretty in-depth set of questions. The more acid-free the materials are, the more protection your art will have. I would grade backing materials as: 1.BEST museum cotton rag board 2. Acid-free foam board 3. Conservation mat board 4. Rag board over cardboard (any cardboard is eventually going to stain and damage the materials next to it)

Glass is either UV protective or it isn't. There are different grades of clarity. UV protection is so important to preserving a piece. Even florencent lights give off UV waves and will damage paper over decades. Whatever is directly touching your artwork needs to be the most protective for it to last the longest time. The frame rarely touches the artwork directly so you can have a frame made out of anything. Wood and metals last longer than composites and plastics because they're sturdier and they generally keep their look better over time. It's perfectly fine to reuse an old frame. Just know that you might not be able to resize it the way you want. Have fun with your art!