i think most people will tell you to apply to at least about 10 schools, including all of your state schools, some "reach" schools and some "safety" schools, as well as any schools you think you might have a good shot at (such as schools who accept a high percentage of out-of-state). although the further along in this process we get, the more we'll tell you that there are no safety schools anyway.
keep in mind, the more schools you apply to, the more expensive it is. i kinda wish my husband had applied to fewer schools (than 10), (isn't hindsight great - he wouldn't have applied to gtown!) but i think most adcoms will think you don't really want to go to medical school if you're only applying to a few.
it's all a balance. find the right balance for you, your financial situation, your likelihood of acceptance at your top choices, and your peace of mind.