Wondering about different CCU plan vocab, and how long it takes to activate

Our closed Alpha comes out next week -- we're going to start with the monthly 500CCU plan and if we go bursty, we'd upgrade from there.

1. When I upgrade, how long does it take for the upgrade to occur? Instant?
2. "messages per room" .. is that the Photon chat? I thought that was a separate fee? Or is a msg an Rpc?
3. Monthly actives? How is this different from CCU?
4. Does hanging outside of a room count as CCU?
5. For bandwidth, it's hard for me to estimate this. If I do "very standard" API calls + once/minute polling for friends list status, I'd likely stay within the 3GB bandwidth limit? That's 3GB TOTAL among all clients per month?

Thanks for the clarifications! Ready to empty my pockets, soon enough.