In the gallery, search under “Dots On Color File Gum Print” you will see an image I posted some time ago on this forum.
While the colors came out ok, I am having some pigment issues with the Phthalo Blue. Their are small blue dots on portions of the print (look in the yellow area under the right bottom edge of the image). I believe the blue pigment had not completely gone into solution even though I mixed it well.
Order of printing for this tri color gum was Nickel Azo Yellow PY150, Q Rose PV19 and then Phthalo Blue PB15:3. Printed on Fabriano EW, that had been sized and hardened.
I am just a beginner and have only limited gum experience but you might want to read "The Gum Bichromate Book” Second Edition, by David Scopick. Also, if you can, get Chris Anderson's Alternative Processes Condensed manual or better yet take her Gum Printing workshop offered at the Photo Formulary in Montana. It is an excellent workshop and you will learn a lot of how Chris prints Tri Color gum.
As you well know by know, everyone has a different procedure. You can print more than 3 layers but I would suggest you try to get your color balance with 3 layers due to possible problems regarding registration, staining and other issues.
Good luck and keep printing.