Ian, wow this work is incredible. And what you have done in your post is quite remarkable and very cool. I looked into the book you recommended (PAINTED LADIES, The art of hand-colouring in photography) and the reviews seem to say that there isn't much in terms of instruction but there are a lot of great artist samples. I just ordered a used paperback version.
I think in the case of "Painted Ladies" technique was way less important than the ideas and end results. You can approach hand colouring in different ways.
Personally, I preferred using toners and dyes, particularly as they left no visible trace on the paper surface. Initially when toning or adding colour dyes selectively to areas of a print I tried using masking fluid, but actually found it easy to work freehand with a variety of fine paint brushes. I would test with saved test strips & scrap prints, and had a variety of toners on the shelf. These included a standard Sulphide Sepia toner, Ilford IT-1, a Thiourea variable toner, IT-4 Gold toner, and alternative bleaches. A Ferricyanide Chloride re-halogenating bleach gives much warmer Sepia tones than on with Bromide, Iodide differs as well. Agfa (Orwo) Rezeptes listed 4 bleaches and then 4 toners for Sepia toning, so you had multiple permutations.
When I used Dye couplers I mixed my own, along with a simple colour developer which was applied by a small paint brush. There were formulae in the mid 1960s BJP Annual, this would have been 1985/6 as I photocopied the page from a girlfriend's father's Annual. Years later I have Annuals themselves.
It's something almost obsessional that you can really get absorbed in. I should have added I used Phototechnology Colour retouching dyes
Ian