M.P.
I do understand your worrying but be careful to not cause the dreaded things to happen by focusing on them instead of on all the good and happy parts of being a teen.
One thing I learned after raising a teen girl is that most things that happen were not as serious as I thought they were at the time.
And if your son is a good kid now he'll still be a good kid as a teenager. He'll try out different behaviours and test you all over again. That's normal. I've seen parent's push their teenager into bad behaviour by being overly concerned and reacting to small stuff in a big way. What is most important is to continue having a trusting and loving relationship with your son in spite of his mood swings and sometimes bad behaviour. Just as he had to learn how to separate somewhat from you at 2 he now has to learn how to make an even greater separation.
I had only a girl and so I can't answer your questions about body changes. But my daughter is also bi-polar and that does make the teen years more complicated. It's important to stay on top of the medication needs so that the doctor can alter the dosage or even change the medication. And it's important for your son to know about the meds he's taking, how they work, and what will happen if he stops taking them regularly or mixes them with non-prescription meds and alcohol. I think now a days it's common for even the good kids to experiment with drugs. I'm not saying that your son will and I'm especially not saying that you should condone him doing so in any way. I am saying that he will be tempted and he is more at risk for negative results because of being bi-polar and taking meds. Education is the best answer.
I want to emphasize that if your son is a good kid now; respectful, loving, and reasonable in his response to life that will continue on into the teen years. He'll want and need to be more independant and there are ways that you can make that happen in a safe way. He needs to learn how to be independant without breaking the rules to prove that he is. The books that you've read will help you learn those ways. What they don't teach you is how to relax and let it happen. That's important too.