To answer the last question; nobody knoooows. Or do we, is it in the PTR? I hope we get talents and chromie time in the pre-patch so I can level all the classes and learn what the frick I am doing without touching SL.
If you have a max level character, it means you can do:
1–60 Chromie time in your favourite expansion
1–10 in Exiles Reach or your favourite starting zone
10–60 in your favourite expansion via Chromie time
60–70 Dragonflight
Blizzard have changed the XP values a couple of times already during beta, including putting them back closer to what they currently are in Live for a time. They could still jack them back up again before launch, but hopefully they won’t.
Actually, they get to avoid that fate and are still pushed into BFA.