The size of the molding is also contingent on the house style, room size and it's age. I have a 1949 colonial with 8 " base molding with a shoe molding at the bottom. Ceiling only has a picture hanging molding(1 1/2"), no crown. New kitchen addition will have a 4 5/8" maple crown with a rope insert. You want the crown molding to be proportional to the room. Ron

You may want to post your question on the Home Decorating forum. I think you'll get a lot more response. The base molding often matches the trim around your doors and windows and crown molding color can vary depending on the wall color. Posting pics of your cabinets and flooring will help. Here is a link that might be useful: Home Decor Forum

You're attempting to use two different trims and trying to make them meet. The upper piece looks like casing, and the lower a shoe mold. It would be best if you used the same trim. However, if you use the casing and continue down the stringer/skirt, you will have an issue when you get to the foyer floor. I imagine you will have the same issue if you use just shoe mold, because sooner or later you will have to transition to the baseboard in the foyer. Don't know if that made any sense, but it's the best I could explain it. Here's a couple photos of using baseboard and how it ties into the foyer floor. There is also shoe mold at the foyer floor. Hopefully these pictures will explain it.

You can either cut the end straight or at an angle and return it to the wall or you can miter the end and return it down to the brown cap piece. The latter wold look better. Here's the closest picture I could find to give an idea of it. http://s901.photobucket.com/user/Rockerdog/media/Astro%20Van/Endcapfail.jpg.html