I think when you hear that people say flat paint for ceilings, they are really talking about flat ceilings....meaning plaster or drywall. Wood is a different animal entirely and a semi-gloss finish is perfectly acceptable. It is still true though that more sheen will bring out flaws so if there are mallet marks in the beams or bad mitres, joints, seams, etc., the shiny paint will make them more pronounced. Personally, I'm good with satin, but how shiny you like it is certainly a matter of personal preference.

Probably be okay if you roll, then brush it. It's more like trim than ceiling, and I always brush out trim after applying w/roller for speed.
Casey