A lot of things have been done to produce these images, and all effects have been applied in a tasteful, professional manner.
With respect to lighting , let me add to Paul's comment. If you look at the irises of the eyes of many of the models, you'll notice a bright ring of light. This is a dead give-away that the photographer used a light modifier called a "beauty dish" (Google it) on his strobe. This produces almost shadow-less but detailed skin. It also automatically produces a characteristic vignetted look, and, if a wall is not far behind them, a weak and very diffuse shadow. Lighting is the foundation of everything that follows, so, as Paul pointed out, this is essential.
The next aspect of these pix that grabs my attention is that there clearly has been a trade-off between global and local contrast (Google these terms). The local contrast has been increased, while the global contrast has been reduced. This can be done in many different ways. A pro headshot studio would almost certainly do this using a commercial PS plugin like Topaz Detail, but if you have enough time and experience, you can get close to the same effect using only native PS tools.
The next aspect that I notice is that the skin on almost all of the models has been prepared by both makeup and in post processing. Again, there are many, many post processing methods that can give this look, but I would look into frequency separation techniques (Google it) and plugins such as Topaz "Clean".
With respect to your comments about use of a "sharp lens", yes, it had to have a certain minimum degree of sharpness, but to be honest, almost any lens could have been used for these shots. Studio portraits like these simply don't demand that much from a lens. They are probably all shot at moderate f-stops (5.6 - 8) at moderate distances, with all the lighting intensity one could ask for.
With respect to your comments about "...use of the the RGB curve and RGB individual color curves are involved, along with an adjustment brush ...", curves are among the most basic of PS tools, and every pro uses them as a matter of course. Their use is unremarkable. The portraits from this studio uses PP techniques that are well beyond that (as described above). One can aspire to reliably putting out image after image of such quality, but it will take a considerable learning curve, and good equipment.
HTH,
Tom M