1) My AP Biology teacher is infamous for giving tests that are so hard that class averages are usually in the 40's or 50's... but she's famous for making the AP exam look easy. In other words, if you have a good teacher, it will NOT be an easy class, and it will be NOTHING like Honors Biology. I can confirm this, since I'm taking AP Bio as a sophomore this year.
2) If you want to do well, it will require at least 1-2 hours a night of reading the textbook (which you could have done without in Honors), massive essay writing, large packets, and extensive review stuff.
3) If you want to go into the medical field, you should definitely take AP Biology, but if you only have an 87 in Honors, you're right... you should wait for junior year, because it's not an easy class. Most of the kids in my class right now that have A's (or even B's) in AP Bio got mid-high A's in Honors.
4) I paid attention in class, studied 4 hours a night, did extra credit, and did all my work, and I have a 106 in there, so it's possible... it just requires A LOT of work.