I am considering taking physics 1b03 in summer school. Can anyone share any advice. I am contemplating solely because of the course content being squashed into 6 weeks. Also, do graduate/medical schools look down on taking prereqs in summer school?

Depends on the school. You'll need to research each school on their summer course policy. Some schools will only accept summer courses taken for extra credit while others just take into account that you did this course in the summer

I'm pretty sure graduate school won't care. Not sure about medical school. It depends on your comfort level with physics. If you are comfortable with it then go for it. If it's something you've been struggling with, it's better to take more time to learn the concepts thoroughly. You'll probably see these concepts again on the MCAT or the GMAT etc. So you really want to get it right the first time.

You can also take other non-prerequisite courses instead (in the summer), and open up some space for the fall term.

Take it during summer school at Mac especially if Mike Massa is teaching it. I took both Physics 1b03 and 1bb3 last summer with Massa and found it relatively easy and enjoyable with him teaching it.