The FAA system is different from UK/EASA. You do not get an ATP in order to become a CFI - is it other way around. You become a CFI in order to build hours to get your ATP. The F1 visa will allow you to train to become a CFI got that reason - if you get your ATP first you would not be eligible fly the F1 visa. The recommended route is to apply for an M1 visa to get your private, then F1 to get your Instrument, Commercial and CFI - maximising your time on that visa.