I would recommend spending time checking out the profiles of students accepted and rejected from various schools, and add in additional time spent researching accepted/rejected profiles of students by major if major is a factor in admissions. If he hasn’t taken any subject tests, he should research the admission requirements for various schools and understand their role at different schools.
While your ds sounds like a solid student, it is wise to stay grounded and be fully aware just how competitive admissions actually is . For example, GT’s 2017 admitted students had a profile of an avg ACT of 33 and 10.6 college courses. Their overall stats were SAT: 1360-1490, ACT: 30-34 // GPA: A, College-level courses: 8-13, Admit Rates= 18% OOS, 45% IS, 23% overall. (Their early action stats were released around this time last yr, so they should be out soon for this yr’s class.)
I would make sure you keep conversations real. He might be well-qualified for GT, but admitted and qualified are not synonyms. Be prepared for the fact that a 34 and numerous APs do not necessarily mean acceptance.
For schools with holistic admissions, compelling ECs, LOR, and essays are going to be strongly factored into admissions. Make sure he applies to a wide range of schools and do not get caught up in the false premise that top stat students will only find peers or be intellectually challenged at tippy top schools.
You might find this PP helpful for understanding how ECs might play a role in admissions. http://www.manhassetsca.org/HighSchool/articles2010-11/DonBettertonpresentation2011.05.17.pdf
Good luck to your ds as he creates his application list. I would encourage him to not hyper-focus on any one school. (In engineering, especially, there is no single school that is going to completely alter his career options in the future.) Create a list of schools across the admission spectrum that he would be happy to attend. That way next spring he is happy with all of his options.