Ed,
I think in the case of figure work I tend to print images small around 8x10 then mount 16x20 with the figure I think it deserves the privacy a larger matt creates. With landscapes I use a much less matt to print ratio, landscapes tend to be more dynamic and take up enough space on their own. The street stuff I don't usually print very large, But I do give them their own space with a larger matt. Then frame color depends on the furniture surounding and weather I want to seperate the image from the wall or not. Also don't be afraid to consider a black matt an black frame for certian prints.