I know many pre-meds, and they all take physics third year. They do chem/calc first year, or do chem/bio. Then, they do either calc/bio and orgo second year. Physics is third year. My roommate is pre-med and she took first semester chem/first semester of bio her first year (at JMU), then took orgo both semesters and rest of chem/bio second year, and is doing physics/calc junior year. Really, it doesn't matter that much other than fullfilling pre-reqs for orgo before second year.
Also, I would only take 14-16 credits first semester. 18 is a lot to handle right off the bat. You want time to be able to relax and get to know college. Take the heavier load second semester.
Also, powderpuff is pre-med i'm pretty sure. Hopefully she can comment..