I'm planning on taking Physics I spring semester of freshman year, and Physics II fall semester of sophomore year. Besides trying to retain the information throughout summer, are there any significant downsides to this?
I think you should be just fine- I did Physics 1 Junior Fall and Physics 2 Senior Fall. I honestly didn't think they built on each other much one was more projections, spinning, motion etc. Then two was electricity, magnetism, and light at my undergrad.