You asked about this specific ceiling. Combined with all that's going on in that room, that ceiling goes too far for me and that's saying a lot. I do love the look of a decorated ceiling and this one could have been spectacular without all of the action going on under it.

Cloudyhaze....I think all of the options look good, but it just depends on the look you personally wish to have for your house, because painting the ceiling white will COMPLETELY change the look. My sister has just bought a place that had brick walls and exposed ceilings that had the beams painted mission brown and the ceiling was in some form of raw chipboard type material. She wanted to brighten the place up before she moved in and got it all painted white. It looks beautiful, but I personally would have thought of other options before painting the brick etc. She got a quote for plastering (sheeting) the sections in between the exposed ceiling beams and it was a lot more expensive than painting. If you are keen to paint just the panelling in the ceiling, then I would get additional quotes. I am no painter but I would suspect if it has shellac on it, it will just need an initial sealer on it, before putting on the 2 coats of flat ceiling paint. I think all of the options will look beautiful, because the high ceilings are the feature.........it just depends on whether you are going for a more rustic look, mid-century look , more modern look...I am not sure of what all the designs are called. Good Luck. Your house is gorgeous. My sister lives on Gold Coast BTW.

If the roof in the sunroom is also flat on the exterior part of the roof then perhaps put triangular windows in the top part of the wall that would look straight outside and then keep the sunroom ceiling flat. You wont notice its different as the window to the outside will be the feature of that wall.

To assist with harnessing the sea breeze suggest a beautiful long narrow feature window that follows either side of the pitch of the roof (which will let in a lovely sky view plus breeze), or just have the top triangle as a window. Understand the desire to have the small window there however in a room with big glass/window features, the small window looks like an after thought and is at the wrong scale.