In my case, I'm 5'3" and about 105 pounds so I'm looking at a 48cm CAAD10. Simply out of curiosity, is a 48cm going to weigh much less than say, a 56cm frame?

It will weigh a couple of grams less since there is less material in the frame. They usually quote the weight of an average size frame. This little bit of weight difference won't make any noticable difference. Any savings may be negated by your choice of components.