If medical school is your ultimate goal, then it's pretty important you take majority of your pre-reqs at a 4-year university. Whatever that looks like for you would suffice - extending your time in undergrad to fit them in, or graduating on time and taking DIY/formal postbacc classes at a 4-year university afterwards. Ultimately, it's fine to major in whatever you want, but if it's not pre-med oriented, you'll end up spending a good extra coin on fitting these pre-reqs in at the expensive, 4-year uni level. If money is no object, choose the route mentioned above that works best for you. If money will be an issue, consider how strongly you want the CS degree and/or options for saving/funding your extra required pre-med courses.
