There is just one RTA as it's done in hardware on the mixer. So no matter how many iPad you have connected, only one mix can show the RTA at a time. There is a setting called RTA Follow that automatically enables the RTA as you select different outputs. For most users using a single iPad this works as expected. But if you add multiple iPad, you will likely want to disable RTA follow on all iPad but your primary. So then as you select different outputs on those iPad, it won't steal the RTA out from under your primary. It may sound a bit confusing but once you think of the RTA as on the mixer hardware, it makes sense. We're updating the manual now with 4.0 info like this but it isn't quite done yet.
I'm not sure I understand what you are describing about the backups.