Coming from a similar situation. DD is taking Japanese in addition to Latin. Mandarin, like Japanese, moves at a much slower pace due to its complexity in writing than Latin or the other more popular western languages. So 1 yr is not going to provide as much language knowledge vs sticking with AP Latin.
To me personally 4 yrs ending with a higher proficiency looks better than 3 +1
If he is not interested in pursuing STEM I do not see a reason to take AP Physics, but I would make sure he has all 3 sciences covered in HS (Bio, Chem, Phys).
Honestly, best is always to make sure you take the 5 cores all 4 yrs of HS (Engl, Math, Civics/SocStudies, Science, ForeignLang).