Some of it depends on your child’s track and much of that won’t be known until they are closer to entering college. My oldest D is a ChemE and entered college with 42 credit hours. Her chosen path was to co-op (she did 5 terms) and do research so the hours allowed her to do this in the normal time (5 years) without over loading her academically (typically around 12-14 academic hours). It paid dividends in better grades and less stress and in the end a good job.
My youngest D went into school with 39 hours. She originally chose a dual degree, Dance and Exercise Physiology. Her goal is to enter a Doctor of Physical Therapy Program. After some consideration she decided she could get her dance degree and complete her DPT prerequisites in 3 years so she dropped the Exercise Physiology major. It did require her taking a summer Physics class at a CC but that was much cheaper than summer classes at the university. It will be close as again not all classes are offered each semester. She enjoys dance so that’s not too stressful though it can be time consuming and she loves biology and anatomy and physiology so that works our well for her. She does have to take more hours, around 16-18 but so far it’s working for her. If she needs to she can add a semester.
Both of my kids chose their own path both in HS and in college. They were very successful at it. In my opinion let your child go their way up to grades 12. If they are capable they will naturally gravitate toward AP courses and possible DE courses. If they choose not to go that direction that is OK too. When they enter college they can choose whether or not to accelerate their degree path. I don’t think that is something to push in middle school. Just encourage them to do their best.