Be sure to check the admissions websites of the schools you are interested in as they may require certain things that others don’t (extra essays, proof of residency, etc.). Great job getting a head start in the SAT! It’s never too early to start working on your essay(s) so I definitely recommend working on a first draft ASAP. Also, start adding colleges you’re interested in to your Common App and filling out the info they each require.
This might be helpful: https://www.coursera.org/learn/study-in-usa
Good luck!