1. Ajax requests are normal http requests. Nothing special needs to be done on top of what you normally have for any http interaction between client and server.
2. Forget about back button. It's a dead end. We are not going to invest our time into it. Our ajax requests do not increase view version, we deliberately disable support back button for ajax. However, for normal requests, you have all support for this two issues from JSF. You can use whatever approach to make buckmarkable pages, it is outside of the scope of Richfaces. I recommend Seam.
3. No problems at all. Use cluster configuration with Richfaces, it will works.
4. What Ajax issues?
5. Richfaces components are part of normal web infrastructure. You can use any technique available on the area. We do not provide any testing gears.

Hope that will help you.