Hello Bob,
Sorry you didn't get any replies sooner, and thanks for all the background info. Hopefully you're still "there", so my comments might be of use.
I too got into leatherworking because of a desire to make gunleather...but I still have yet to make my first holster. I've gotten distracted by other things like pen cases, billfolds, etc.
I definitely recommend Stohlman's holster book. It will show you some essential concepts and techniques like pattern making. You can extrapolate his ideas and adapt them to your ideas. One thing to be aware of: The book is big. Not heavy or thick, just large, something like 11" x 17". To fit it in my bookcase, I keep it folded in half.
As for tooling...I'm on that quest too. One book I will probably get is Stohlman's "Tech Tips". There are also some tutorials on YouTube if you search around, and for specific questions once you've gotten started, this forum is of course an excellent resource.
Good luck with your leatherworking endeavors.
Mitch