No doubt, there are many books, online tutorials, and actual classes available learning orportraitura and photographic lighting in general. I'm sure many of them have much to offer to anyone who is willing to learn and improve their photography.
The only things I find problematic with some of these resources is that many of them place too much emphasis on equipment and certain brand names and not enough emphasis on basic and essential theory. Of course, we all need to be familiarized with the "tools of the trade" and what is available on the market and which types are most applicable to what we are doing ,however, when we understand all the basics of lighting along with posing, composition, and post-processing, we will all know enough to make the correct equipment choices based on all the underlying theory and knowledge.
Sometimes I compare photography to other disciplines such as writing and literature. Imagine a creative, artistically inclined, and the knowledgable person wanting to become a writer, a poet, even a technical writer and suddenly realizing that he or she is seriously deficient in basic grammar, spelling and ordinary composition (like me)! So... they go out and purchase a high-tech computer word processing system with all the bells and whistles and still experience problems, issues, and frustrations because of their basic deficiency. That's why I recommend Zeltzman lessons. All the basics are there and they transcend film, digital and whatever medium is coming in the future. Light is light, posing and human body mechanics, composition, placement color usage, contrast, and all the other aesthetics remain the same regardless of the materials. Most of the film technology as to dynamic range, exposure, lighting ratio, angle of incidence and sensitivity can be easily correlated to digital theory- there is usually equivalent theories or processes that are common to both.
I advise folks who are learning photography NOT to "join a cult" and worry about emulating the exact style of their teachers. First, learn the theory and adapt it to your own psychological and aesthetic approach.
There is a trend in learning photography to "run before learning to walk " and a preoccupation with equipment acquisition. When a lighting question arises, here on this site, there is usually an immediate flow of well-meaning responses suggesting all kinds of lighting gear- beauty lights, umbrellas, softboxes, Octoboxes, and much more. It's almost difficult to believe that many of the iconic portraits we all love and discuss, made by many of the grand masters of photography, were made with a simple flood lamp in a 12 or 16-inch metal parabolic reflector and a set of barn doors- perhaps a spun glass diffuser- nothing more than a bright light bulb in what looks like a metal bowl or by the light of a window with exposure to the northern sky- perhaps even a candle.
Many decades ago when returning from the service, I SPLURGED, and spen 2 months at the Winona School of Profession Photography to brush up on my "civilian' photography. I was fortunate to have 3 of my favorite portrait teachers- all doing work that I greatly admired. The first guy did EVERYTHING with 2 umbrella units. In the second class, the teacher was running a dozen lights, and in the last portrait class- the teacher never entered a studio and did everything with natural light. Enough to confuse even the best of students- let alone me! Thing was, the approaches and styles were very different but the underlying theories had more similarities than differences. That was one heck of a good experience.
PS. Regardless of geographic distances, ONLINE brain-piking is always invited- keep in touch!