I had similar questions and found the same issue, there isn’t a “path” to this cert.
It’s much less about the flying, and mostly about the teaching and delivery. Yes, you have to fly the maneuvers from the right seat to commercial standards, but the real thing you are tested on is how you teach subjects.
The CFI PTS is the starting point. You have to be comfortable with the ability to relate the material outlined in the PTS. While you aren’t expected to memorize everything, you need to know how to organize yourself, prepare a lesson, and deliver.
Focus on this and practice teaching every opportunity you get. Ask existing CFIs if you can help teach a ground lesson. Find another CFI candidate and practice on each other. Practice flying, talking, demonstrating, all at once. Find a non-pilot friend and teach them something (this was really helpful to me)
The FAA handbooks referenced in the PTS (PHAK, AFM) are the place for the technical material. For example, you will be expected to discuss common errors and corrections for maneuvers, and this is taken right from the AFM and referenced in the CFI PTS.
Remember that as a CFI, someone will walk into the school and you will be their first contact with general aviation. They will get in the plane and try to steer it like a car… because that’s what they know. You have to be able to teach this student as well as an experienced pilot.
Unlike other ASA oral prep guides, I didn’t find the CFI one to be very helpful. I found that I was relying more on the Commercial prep guide, and then drilling FOI material based on the PTS.
Enjoy it. It’s a real learning experience.