In contrast to Jim, and as someone who took such a rigorous schedule in their Sophomore year, I recommend the AP and Honors classes for a couple of reasons.
My schedule was thus:
Honors Algebra I (I had completed Honors Geometry as a Freshman)
AP European History
The first thing to note is that many colleges and univeristies (certainly all of the colleges and universities that I looked at) grade AP and IB classes on a 5.0 scale. Thus a B in an AP class is equivalent to an A in an non-AP class.
Secondly, the material in the non-AP class is not necessarily easier to learn. Often it is the exact same material, out of the same book. If your son's issue is not comprehension or ability, a lower ranking class will not help; if anything, it will make it worse, because instead of learning discipline to not procrastinate, he can submit a project against a lower expectation.
Also, AP classes come with an AP test (which your son apparently does well with), which many colleges will accept for intro classes. I started my college career with 20 credits this way.
Contrary to Jim, if your son plans on going to university he will probably have to take a bunch of classes he does not want or need (Thank you, SO MUCH, GE requirements shakes fist). I was a CS Major, and I still was required to take 20 units of english-style classes and 15 units of history/sociology classes in order to complete my degree (which my AP classes' credit helped with). Wonderful things to get out of the way now, or at least get a grounding in.
Additionally, my experiences with AP classes were excellent in terms of the skills training that they provided, rather than the material knowledge. AP History (European and later US) were wonderful exercises in drawing conclusions from evidence and defending one's position (it was required for the AP exam). I would recommend it for anyone planning to take higher level science courses.
Finally, learning to deal with large amounts of work, budgeting his time, and prioritizing activities (even important activities such as classes, homework, and projects) against one another is a vital skill, both in higher education and outside it as a general work and life. It is, in my opinion best to start it now, rather than in college where one also has to balance things like food, and paying rent into the equation, and were a mistep can set one back months until they can retake a class.