When you have the medical professionals on board to document that the health issues are unequivocal, you should not have problems getting what you need and don't be afraid to ask. Over the years, my oldest was offered everything from a partial school day to just skipping the first couple of hours (so he can sleep in) or leaving early as needed to unmarked absences and naps during the day at the nurse's office.
I would definitely reduce homework and busywork but not necessarily courses he wants to take. You'll have to write it into his IEP and still work it out with his individual teachers at the beginning of the semester after they provide the syllabi and adjust periodically as needed.
