1. I belong to the school of thought that says crown molding should be a consistent colour throughout your home. Unless you have a lodge or cabin-type home, painted white, ecru, etc. is usually best. 2. Varying colours of white or varying strengths of paint on a vault or on the tiers of a tray ceiling give it an interesting depth. I personally don't care for tray ceilings that have some of the tiered surfaces or the sides of the tray painted with the wall colour or a contrasting strong colour. Just my opinion. 3. If you're considering painting the walls a darker colour at bottom that fades out towards the top, I can only assume you don't have a very formal dining room, although the dimensions you give would belie that. Your room size is nice and large, and a chair rail would not box anything in---it is really what one expects to see in a large dining room. It also allows you to "logically" paint one colour below the rail and another above. Good luck with your room!

My living area has trusses with 1x10 pine boards that are exposed. I originally painted them white in flat, since it is a "ceiling." However, about 1 year latter I went up there to dust the trusses and the dust just smeared more! I wound up repainting everything (trusses and boards) with standard bright white satin from Glidden. I love the glowing sheen. I think satin will work just fine for your case. If you happen to have pine boards with knots, use oil primer or BIN sealer for the knots. Otherwise, the knots will bleed into the white paint.

I'm not a fan of semi-gloss. If there are any imperfections in the wood it will show up. I would use the same finish as the trim, a satin. Use flat on the ceiling and matte on the walls. It is going to be a beautiful room.

Do everything except trim in flat. I was skeptical when my paint contractor suggested this, but it’s turned out well. Flat is no more difficult to clean and is easy to touch up. Also, flat minimizes flaws and that dappled texture that annoys some people.