You'll have to do it in the opposite order. In order to hold a FAA CFI you need to hold a FAA commercial. In order to apply for the FAA commercial you need to hold a FAA private. You'll also need an airplane IR. You can get the FAA private under 61.75 as a paper shuffle between your CAA and the FAA. Then you'll have to get the IR and commercial like any other FAA applicant. Training, written test, checkride for the IR and then the commercial. You'll need a total of 250 hours before you take the commercial checkride. Then there are two writtens and a checkride for the CFI. Don't know how it is now, a few years back ~75 percent of the initial applicants for the CFI failed the checkride. I've heard of the oral exam going for 5 or 6 hours before they even got in the airplane.
Last edited by MarkerInbound; 31st May 2016 at 16:17.