For headshots, KEEP IT SIMPLE! A headshot is a photo/model agency etc., slang for a portrait. People want to look good and possibly flattered in their headshots. They do not want the distortion that can be introduced with the use of a wide-angle lens. Any experienced portrait photograher (like me
) will attest to the fact that a medium longer focal length lens is best for portraits, especially in head and shoulder and close shots. For a full-frame digital camera, I recommend a 105mm lens or thereabout or the equivalent thereof for whatever format you select.
The recommend focal twill enables you to work at a distance that will not introduce distortion. Perspective is controlled by distance so the focal lengh accommodates a comfortable and optical correct working distance, and good composition is best.
If you are mainly a real-estate shooter, the 85 to 105mm range, in a prime lens will not serve you well in any kind of architectural or interior work, except perhaps in shooting small decorative or structural details. If you acquire a zoom lens that encompasses that longer range, you may find it more economical. A PRIME 105, however, is an excellent choice as per image quality.
Whether you go DSLR or mirrorless is up to you. Good lenses are available for both systems. It seems that the manufacturers are all trending toward mirrorless production. If I were retooling at this point I would go mirrorless, keeping in mind that lens production and availability, software support, and warranty service will be available for the longer term. The newer mirrorless models will probably serve you better in your real estate work, especially in difficult or contrasty lighting situations- more pixels, better sensors, l and likely better dynamic range than some of the older DSLRs.
I have been doing photography professionally for a very long time so I am not affected by GAS unless I overeat my favorite baked bean recipe. I haven't come up with a nifty, cool, pithy, and slick acronym for word for my equipment acquisition philosophy to replace GAS. My concept is "the right tools for the right job and anything else is extra baggage and dust collectors. If any of y'all out there come up with a good word, let me know- we'll coin a phrase together!