Regarding courses: Should I switch out Spanish III, IV, and AP to take more AP classes?

It's far more important to the top 20 schools that you have some mastery of at least 1 foreign language so I highly recommend sticking with Spanish and taking it through AP Spanish. While many schools state on their admissions website that the language requirement is 3 years, keep in mind that this is the "minimum" not what admitted students have on their transcripts. It's far more common that admitted students to T20 schools have completed their language requirement through AP/IB levels and some have 2 or more languages on their transcript.

No admission officer at any T20 school including HYPSM cares if you have 18 or 20 APs completed. IMO that is complete "overkill".

What they care about more is that you show evidence of intellectual vitality in academic areas that pique your interest and talent. So if you are interested in astrophysics for example, they want to see that you sought out college courses in astronomy, astrophysics, advanced physics, and higher maths to support this interest of yours. They would appreciate seeing that you also looked for internships in this field of study as well as attempted to generate research into these topics with experts or professors who teach this subject. Lastly, exploring social media outlets to bring awareness to astrophysics like YouTube channel or TikTok channel also supports your academic spike narrative.

Anyone who has very strong "spike" narratives or "intellectual vitality" will have a clear advantage over someone with 18-20 APs regardless of class rank.

Getting into a T20 school is NOT a meritocratic process. You have to read between the lines when you evaluate each school's criteria on their scoring rubric and figure out how to position yourself against the thousands of applicants with perfect GPAs and perfect test scores. Remember there are over 4000 valedictorians who apply to Harvard each year and perhaps only 400 of them or less get in. Why? Harvard wants a well-rounded class of cohorts that includes recruited athletes, legacies, development candidates, faculty children, VIPs, and hand-picked ones that the dean selects. Harvard believes in diversity and therefore also selects a number of low-income and first-generation students. Even though affirmative action is not allowed in the criteria, selecting students from poor zip codes will become a sort of proxy for admitting black and brown kids.

Whatever internal battle is going on at your high school for King of the Hill really doesn't factor very much in who gets into T20 schools. You are not only competing with your classmates but super entitled kids from Exeter, Andover, Choate, and Deerfield who have a 25X upper hand in probabilities of getting admitted to T20 schools even with lower GPAs and Test scores.

Good luck and shift your focus on differentiating yourself from the pack.