Which iMac for Photo Editing?

Since you seem unsure of your own ability to choose, I will recommend option 3. Go for all the power you can get!

I wont tell you what to get but I will say there are some things to consider before making your final purchase -

Photoshop LOVES RAM and given your camera and most likely working on RAW(NEF) files, the more RAM the better as RAW files can be rather large and depending on edits, a fair amount of "history" built up in the app.

To get the most out of images, you will want to create a colour profile for your iMac choice. (Some refer to it as software calibration.) You'll want to consider a good 3rd party tool such as Spyder, Munki etc. You may want to investigate which tool works best with an iMac (from your options).

Option 2, a balance machine is better than a machine with bottleneck at somewhere.

Option 1 the CPU is weak.

Option 3 too less RAM for photoshop.

12G RAM is good for photoshop. Of course, the more the better, but the performance increase from 12G to 16G is not that much.

And the i3 CPU has quite good clock frequency with 4T available.