A 142 school waves their magic wand and you is one, at least for their purposes. 142 does say you need a CFI if you're going to instruct in an aircraft but that's very rare in the 142 world. If you're instructing leading to a commercial rating you just need to meet the experience requirements for a commercial, if training for an ATP the instructor has to meet the experience requirements for an ATP. In theory you could have a 1600 hour private pilot play G 5 instructor. I don't know how it is now, 20 years ago FSI would hire you as an instructor without any time in type. Simuflite was always big on saying "Our instructors have time in type."