Some of the best pilots and instructors I know are retired law enforcement.
For the CFI training, if you can do it locally, do it.
It's great that you have the commercial and instrument already.
For the CFI training, if you can do it locally, do it.
For your fundamentals of instructing and airplane flight instructor written test study material, you could use a company that begins with "Gle" and ends with "im".
Or, get the material straight from the horse's mouth:
FAA - Aviation
FAA - Education & Research
(Your tax dollars have already paid for the training material.)
For the multi-engine training, you may consider one of those $1,500 two or three day courses.
Network at the local airports, part time instruct and see if you can find another pilot that needs multi time and share/safety pilot that valuable time.
Now a days, 31, 41, 51 or even 61 isn't too old.
Good luck.