Trig is very important for pre-calc. If Trig is a full year course, it probably also includes early calculus and the school's AP Calc class will be adjusted accordingly. AP Calculus BC is a full two semesters of a college calculus class. I would not skip the prep for this class. Can you find out what topics/book the pre-calc class does? Is there an honors class that goes more in depth.
Another thing to consider is what he takes after Calc BC. In my DS's H.S. the only other math options are AP Statistics and AP Computer Science. Would you plan on him taking courses at a local university?
As to skipping to AP Bio.. I personally would not recommend it. My DS's school does not allow it. In my school you not only have to take biology but chemistry (non AP) before you take AP Biology. The AP Biology class expects this and skips or glosses over topics the kids already know. There is a huge amount to cover in that class. I know kids at DS's school that took Calculus as a freshman, but our school doesn't let even the top gifted motivated kids to take AP Science until junior year.
What is your goal with pushing a lot of AP's in 9th grade? Are you looking at having him graduate early? Start taking classes at community college. I would look at his whole H.S. career and how much homework this is going to involve. If you are concerned about GPA, I would NOT try and push him into AP classes in 9th grade.
Good Luck.
