An outstanding professional photographer, writer (he has authored several books on B & W) and educator, Harold Davis always takes raw color photographs and converts to B & W during processing. According to Harold Davis, the manner in which the color photos are processed, by his set up cameras, is critical so that when he convert to B & W the processing is more accurate. Harold has several youtube videos on B & W you may want to checks these out.
B and White, Texture, Tone and Contrast. I like #3 the best.
I focused on the leaves on the far right of your ISO 100 shot and these leaves are the clearest of all your ISO's. Of course it could be a focus issue with your ISO 400 shots , however, if your focus was right on in all your shots the leaves are clear in your ISO 100 shot.
I use my Nikon AIS 105 F2.5 on my Z6 with the LTZ adaptor with peaking and this lens works extremely well.
I have taken a photo from almost the same spot, however, your photo is considerably better especially with the mean sky.
Very nice tonality and the cloud structure enhances the photo.
Wonderful landscape shot.
Thank you for the link. The Rabbi is very enlightening.
I would add Adam Gibbs Landscape Photography to your list.
I do not have the Nikon 24 to 120 lens. However, my favorite landscape photographer, Adam Gibbs, reports that this Nikon 24 to 120 is his most used lens.
My first Pfizer shot gave me a sore arm for two to three days. with my second Pfizer inoculation neither experienced a sore arm nor any side effects. Great experience with the vaccines.
Another option is to purchase the Fuji XT-4. This ASPC Fuji is relatively light, stabilized, great color rendition, considerable less expensive then most of the other recommendations and very good battery life. I would add the Fuji 18 to 55 2.8/4 lens.
With the Fuji XT-4 you can add other lenses when you return from your travels.
I still shoot my F4 often.
Nikon will be coming out with the d500 upgrade in 2021 the 580
try focus peeking for manual focus lenses.