Flat paint looks dirty pretty quickly and is hard to clean. I'd recommend satin on the walls, and something slightly glossier on the trim. I've been using high gloss oil on the trim for maximum shine and durability, but I have an old Victorian, so it goes well with that. I've heard that Sherwin Williams has a new water based 'oil' paint, whatever that is. I've tried a lot of paints, and find Porter to be the best.
This is what I recommended to him. I usually dislike high gloss paint on interiors. Water based oil....?