Fist Class ("Flagship First") is the eight seats in Rows 1 +2.
Business Class is Rows 3+4 - separated from the F cabin with a curtain, and from the rest of the very large business class section by the galley, lavatories and the space for the L/R 2 doors through which boarding is done. This feels nicely private.
3A/J are my preferred business class seats on this aircraft. 4 might get a little noisier because of the lavatories behind them.
Speaking of lavatories, the one behind 4J is 'handicap accessible' and markedly larger than the other ones. Also, the self-service snack bar is set up right behind this area, so if you want to have a bite in the middle of the flight it's not that far of a walk :)

edit see this here on an accurately-drawn-to-scale map that's much more detailed than the seatmap on the AA website: https://www.aerolopa.com/aa-773

Okay thanks for the info!

that drawing is great! It’s so detailed and accurate!