Droste, the FI rating is no easy walkover. I think you need to be psychologically prepared for this. It's not a rating for accumulating hours or showing off. You really need to have a temperament to care for students. If you're a picky or apathetic type of person, you should think twice before spending money on the rating.
MakeItHappenCaptain, rotary FI ratings require 400 hrs total (not command). The rules say you can apply for the rating when you have 400 hrs total while the rating itself requires a minimum of 40 hours. Most students therefore start learning their rating at 360 hrs total.