750 and the 800XPC is the same rating. It's essentially is the same aircraft.
CE550B is correct, the 4000 is a new rating.
From what I have heard, there'll be no FOs on the 7X for a little while. Captains need to get experience and time on type.
An example of this is the new policy for the G5 is for new captains (who may not have a lot of international experience) to do 6 months or so in the RHS gaining experience before moving across. (Command pay in the RHS)
No idea how the 4000 will be crewed initially. It's not here yet. I dare say there'll be a little bit of captains only as they get experience on type. So for this year, new FOs can probably forget the 4000 and the 7X. (**this is my guess only**)
Those in the know might post or then again, I think they're a bit busy trying to get manuals written.