I've been reppin' this style since forever, 'bout time someone appreciates it--> For "sexy casual" love the grey sportcoat, navy/white gingham check shirt and dark jeans. Make sure he gets them hemmed! I will pin each item separately too
Cheat sheet: what color shoes go with what color suits. These are guidelines. If you want to make a fashion statement, a light or dark brown pair of shoes would go great with a navy, blue, or light grey suit.
So many guys make this mistake. Most dress shirts are simply too long and usually a full cut in terms of silhouette so they should be worn tucked in. A trim fit cut is a start, but at least shorter tails if you want to wear it untucked.