Here are a few more reviews to help you understand the system.

https://youtu.be/nHhCQm14VRc Gerald Undone

https://youtu.be/L833ZhUtiBw Tyler Stalman

https://youtu.be/tyLV5-zMXd4 Tony Northrup

THE HOAX (A short film made with the LUMIX S5IIX + ATLAS MERCURY ANAMORPHIC LENSES):

https://youtu.be/jHaDXTNYQR8

“We are switching from Sony to Panasonic” https://youtu.be/ouVFlMx-83Q Larimore Studios

https://youtu.be/7XNIR62fYaI The Hybrid Shooter review

https://youtu.be/jfTHLX9Joig Josh Cameron rant (He has a ton of special videos on the S5 II and IIX cameras)

The Sigma MC-21 Mount Converter/Lens Adapter (Sigma EF-Mount Lenses to L-Mount Camera) is a $250 wonder that can mount Canon L glass to the L mount cameras. Apparently, from some reviews I've seen on YouTube, hybrid PDAF in the S5 II and IIX works well with them.

Leica, Panasonic, and Sigma are all FIRST PARTNERS in sharing the L-Mount specifications. Sigma makes 29 lenses that fit all L-Mount cameras. Those greatly expand the 13 Leica and 14 Panasonic offerings.

The two 24-70mm f/2.8 lenses you mention are both excellent options if you stick with the D500. Choose based on price. The Nikon will have better resale value. The Tamron is less costly. I doubt at 21 MP that you would ever tell a difference, although the Nikon lens may focus a tad faster.

BUT:

If you move to mirrorless, and want to expand both your video and stills capabilities, my recommendation is to move away from both APS-C and Nikon.

If I really wanted to do real estate video in addition to stills, I would not hesitate to forget Nikon and get the Panasonic Lumix S5 Mark II, which is a TRUE hybrid (stills and video) camera capable of cinema-like results. It has fantastic in-body image stabilization features, DUAL stabilization with certain L-Mount lenses, phase detect hybrid AF, the ability to record true log video, anamorphic video, four channel audio capability, and more. Body is $2000. It doesn't get any better for video and full frame stills at that price.

DOZENS of reviews of this camera can be found on YouTube. I have tried in vain to find a BAD review of this camera, and haven't seen one yet.

> https://youtu.be/eDAKWDK3H8E — Emily at Micro Four Nerds reviews the Lumix S5II (about 14 minutes)

> https://youtu.be/A06GnDOx0vE — Hugh Brownstone at Three Blind Men and an Elephant reviews the Lumix S5 II (about 27 minutes)

> https://youtu.be/FYebjEgf3J0 — Gerald Undone reviews the Lumix S5 II (about 25 minutes)

> https://youtu.be/WjvZgZSpRWU?t=99 — Panasonic's Lumix S5 II and IIx introduction at CES (Warning: about 50 minutes, with parts full of geeky specs that some of us drool over)

> https://youtu.be/Y5auV2JC7fc — Richard Wong Reviews the Lumix S5 II (Very long 1:38, thick Asian accent, but THOROUGH review with many great comparison tests)

I can attest from seven years of using Lumix Micro 4/3 gear that no stills camera company puts better or easier to use video recording features in their hybrid mirrorless cameras. Panasonic's S5 Mark II has solved their only major flaw — mediocre continuous tracking autofocus — spectacularly well. You can see many tests in these reviews.

All S5 Mark II reviews on YouTube: https://www.youtube.com/results?search_query=Lumix+s5+ii+reviews

FIRST PARTY L-Mount Alliance (Leica, Panasonic, and Sigma) lenses are available for the S5 Mark II. Here is the mother of all lists for them, and some other brands:

https://lesdeuxpiedsdehors.com/en/lenses-for-l-mount/#lenses-mount-l-full-frame

Another long list of compatible lenses: https://alikgriffin.com/list-of-l-mount-lenses/

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!

I have not used the D500 for video. I use it for bird photography because of the buffer rate and high frames per second and autofocus. I use the Z6 for everything else, but especially for video. I used to use my iPhone for video but decided to up my game with mirrorless. If I only wanted one camera for video, birds, and everything else, I might be tempted with the Z9. Nikon has a sale going on now and offer some good prices on camera bodies. If I had extra money to spend I would consider getting the Z6II for video.

I feel your pain, literally. I did an event last weekend that was 4 hours long. I had two cameras both mirrorless and a flash hand held on a remote trigger. I used my Z6 as the main camera and the Zfc for some casual shots. Next time I will have one or two other photographers help with the event. My work is done for a non-profit and pro bono. When I shoot video, it’s mostly as a documentary and I have my camera mounted on a tripod with an L.E.D. Light mounted on a light stand. I use wireless mics. So far I have not seen the need for an external monitor. So far the non-profit is happy and so am I. I am retired, so my cash flow is fixed with no extra money for gear.