Bear in mind that Cannondale uses the BB30a standard, so not compatible with 24mm Shimano cranks unless you use an adaptor. The CAAD comes with so-called midcompact 52/36 FSA chainrings on the 105 setup and a 11-28 cassette. That should be perfectly fine for you. Any lower, and you have to purchase a long-cage derailleur to accommodate a 32 cog. Not worth it in my opinion.