For anyone contemplating doing this, I’d suggest that you study up and pass the CASA PMI exam first. The PMI exam could be quite difficult to pass without doing any pre study. Once that’s done, focus on building “your own” lesson plans. The bulk of the work in a FIR is being able to learn how to develop and give good briefings and debriefings.
It’s certainly not a walk in the park and it requires quite a lot of dedication, particularly for someone older regardless of experience. It’s a completely different mindset in my opinion, from being a line pilot in a multi crew environment.
Good luck for anyone contemplating on doing this, the industry would certainly benefit from a few more experienced people getting into training.