I did not reasearch how the original was painted...and I have no idea how to go about that. Besides "more has been written on this subject than is known"...if you get my drift
I trusted my eyes and common sense was my guide. Because of the way it looked to me, I asume that the face and hands were underpainted. I did this with raw umber plus white in order to get a likeness and determine light and shadow. Then I glazed and scumbled over that to make skin tones and began to build light into these wet glazes.
I blew up my reference material (via Xerox machine) and traced a copy of my drawing from that onto the canvas. For the most part, the rest of the painting was painted a la prima. Then I used many glazes over that to make the colors as dark and as rich as possible (since you can't get a la prima painting to look that way without help).
I used a lot of layers, partly to get that "look" and partly because I messed up and had to use a layer to "correct" the one beneath. I made at least a hundred layers, but I am sure that Hals did a lot less....
I have been fortunate to have seen some Frans Hals paintings in museums "up close and personal". I am convinced that he worked in the method described above....underpainting face and hands. I think that, by the telltale signs I've seen in his work, that underpainting, for him, was the foundation for his virtuoso performance with a brush - even though it sometimes appears like a la prima.
Basically, I just did whatever it took to make my copy look as much like the original as possible.
Hope this helps.