If you want to be a FI then probably nothing will put you off but don't expect to make a living out of it. FIs come from 3 sources; aspiring airline pilots who can't get a job and want to keep flying. They have already spent a large sum on their qualifications. Retiring pilots who have had condiderable time in aviation and can afford to be an FI but expect nothing back other than the flying. Thirdly, those who belive they can make a career in instructing; they struggle then economics takes over and unless you have another income they either go to the airlines or give up. Hence the ATPL versus CPL exams.
Microlight instructors do seem to make a living out of it! If you feel you must do it, try to treat it as a hobby and have a source of income to support it; you will probably never recover the cost of the qualification.