I'm a chemical engineering major, here. I got accepted to UCSD, but mostly waiting back on UCB as my first choice school. My school offers a lot of the prereqs, but only during certain times each year and they're a pain to take with everything else.
Personally, I think it's not too bad to take calc, physics, and chem at the same time. Currently, I'm taking honors O. chem, electric and magnetic physics, calculus, and java. It's time consuming, but I wanted to take Quantitative chemistry at the same time (I believe my CC is the only one that offers it in California), but turned it down due to 20 unit madness.
As a student though, the classes are only challenging if you don't like them. If you enjoy them, then you hardly notice any problems.