@KRoundy I think you have that right. For (b), I like what @ColeGiacopuzzi said in reply to one of my recent posts. Think of it as standing up as you cross centerline. But you are right, do not lead with your upper body. And, of course, your edge change will not finish until you are well past the spray line.
When I picture my body hitting centerline, I picture myself allowing my body to get pulled up by the boat, but I make sure my ski's path is not changing.
I'll use Joel Howley's slow-motion video of 41-off (because we're all trying to fine-tune our -41 passes, right?!). 😉 Seriously though, notice that he is just starting to stand up as he crosses centerline. He doesn't even get to a flat ski until he's way outside -- way out there before he allows the ski's top to be visible from the boat.