Well... First, I'd try to talk you out of the crown moulding idea...
Then I'd suggest blocks for your corners and your transitions but if you get too elaborate, the crown will make the rest of the trim in your home look kind of plain.
Last, I'd suggest making the bedroom ceiling look like a vaulted tray ceiling. Run the crown level from the lowest points of the ceiling and paint everything above the crown to match the ceiling.
As if that weren't enough... You could stop the crown at the verticals with returns on the exposed ends and butted against the walls in the short corners.
Crown run to match an angle rarely ever looks right but over your stairwell, you don't have much choice.