Welcome!
1. I think an archival binder is ok but if there's a lot, that could lead to bending. For my Gold HOF postcards I put them into large toploaders and put those into a file holder I got from Staples.
2. There's been a lot of controversy with TPA's over the years. The best bet is to talk to people here and more importantly, study up on your own. I HIGHLY recommend Ron's book:
https://www.amazon.com/Baseball-Hall.../dp/078647050X
3. As stated before, there are some premium items here from time to time. Other than that, see what I said on #2. Using the search function can also help as people have identified certain forgeries on here.