Can anyone help with this?
I have my own ideas – but just would appreciate some guidance on the "best practices"
Well, I don't know what is the best practice, but I would do it like this:
Image > Duplicate and move the two windows next to each other to use one as a reference.
Image > Mode > Grayscale
Image > Mode > Duotone, and set the options similar to the screenshot below. Clicking on the color swatch gives you the picker when you move it over the reference RGB image so you can sample it to find the closest Pantone color match. Clicking on the curves gives you the the Duotone Curve ink editor. Click on the curves to add points and drag them up/down, clear the respective fields to remove points. I made a quick try but you can spend more time and mach better the color appearance and shading by fine tuning the curves and trying similar Pantone colors.
To open the Duotone Options window again after closing it choose Image > Mode > Duotone again. At the end after done, if you don't trust your printer for this you can split the duotone channels yourself by choosing Image > Mode > Mulitchanel. If you like you can also check Show Channels in Color in the Interface category of the Preference to visualize the printing passes in color when you display only one of the two channels in the Channels panel.
click this image to see larger