Some programs like to see an applicant's prerequisites completely done to even be considered for an interview, some don't. It all depends on which programs you look at. In my honest opinion, finish all your prereqs first and at the same time get the healthcare experience/shadowing, etc. Just doing all the paperwork for CASPA takes enough time itself. One year more isn't a long time to wait, you don't want to be burned out from taking prereqs before you even start PA school.