Windfront/breathable back, sounds good. As for the rest, as long as they don't fall down, you're probably all right. Give 'em a test ride to be sure.

The bunching bit is more an issue of construction than size. If they have an articulated or contoured knee, they're less likely to bunch. And right now, you may not think you care about bunching, but by halfway through the winter, you can get pretty sick of it.