#1 Unreal Studio sits on top of UE4, so you’re not missing anything.
#2 The plan is to keep things this way. We’re not trying to trick you into doing something you’ll regret.
#3 I don’t have a crystal ball, but there is no plan take anything away you already have in UE4. How could we possibly answer this question for an infinite future? What is “core” to you might not be “core” to the guy next to you.
#4 Pretty much in sync, but we have to lag a little (weeks) to make sure of quality in Studio features. Previews of Engine will often include some, but not all Studio features. Previews won’t be complete (per definition).
#5 Don’t know. Probably need to be very specific about what you’re talking about and give a clear example.