Check Sunset Western Garden Book.

Clematis will grow just about anywhere, but I would reconsider the south facing wall because of reflected heat. Where I am, clematis do well if they have no reflected heat, and plenty of water. With too much sun on the flowers they will wilt badly and burn up. I grow mine under a tree where it grows upwards through the branches, gets no reflection off walls, and the roots are shaded by a large boulder set far away from the stem. It also is between the house and a block wall, which block the sun in the hottest part of the day. Check out this site, and even though it's Australian, had tons of great info.

Here is a link that might be useful: Great clematis site