[Zeke]

As I said, exterior 'flat' is not truly flat. But in my 48 years in the trades I never met anyone that wasn't a painter. Most don't like to paint, but if you ask them about painting, they know all the answers.

For Smooth wood on the outside, I use one or another of the 'sheens'. On trim I use semi-gloss or even gloss on the entrance doors. That is is they are perfect or nearly perfect as gloss shows every little imperfection. But don't even kid yourself, satin shows all the defects too, just from not as far away.

Textured or grained wood and stucco look like ass if they shine back at you. YMMV.
You can always look up the pdca.org or architect's associations for guidelines that you won't find on a car forum.

The bottom line: paint it anyway you wish, just use good paint.