@Culciambo

The F1 visa option only works if you were starting your pilot training from scratch . Because you need to spend about 9 month to a year in order to be eligible for OPT

By going on an F1 visa only to obtain your CFI ratings wont be long enough to qualify for OPT which would allow you to build some experience

The other option would be to enrol in a college degree and work as a flight instructor on the side . The F1 visa allows you to work for 20 hours a week
Some flying schools in the U.S have this option like Dean International , Aviator College etc