Which mac mini should I replace my 2013 27" iMac with?

I went from a 2013 27-in iMac (Core i5) to a 2020 M1 mini, and just traded the latter for a new M2 mini pro with 12-core CPU, 32GB Ram and 1TB SSD. I am still using the LG 32UN880-B 4K Ultrafine HDR display which was a revelation after using a 27-in iMac. The LG has manual controls with a joystick which I have overlooked in my case because of the display's articulating Ergo VESA mount, but a do-over would seek a display with galvanic touch controls on the side of the display.

I spend most of my day in one browser or another, stream video content, and use non-Adobe (e.g. Affinity) tools, so I felt the configuration was justified for the tools that I use and allowing for the inevitable future growth in the operating system and application resource demands.

Balance your budget with future needs. The Apple Silicon Macs are not upgradeable after purchase, so plan accordingly now.

If you are running Catalina on that 2013 iMac, then you have already dealt with the 64-bit application requirement, and if still on Mojave or older, you will have to determine what remains as 32-bit (e.g. free Go64 app), and if your third-party application vendors have 64-bit versions of their applications that are stated compatible with macOS Ventura. Same drill for printer/scanner vendors who may or may not still support their device drivers on Ventura. Networked devices may be supported by Apple's built-in AirPrint as an alternative to missing vendor drivers. At any event, you will likely need to set up your printer/multi-function device again.

You will need a last Time Machine backup from that 2013 iMac, and you can have that mounted when you perform the initial setup of the new Mac mini as that will allow a smoother and more punctual data migration than waiting to use Migration Assistant between the iMac and the mini afterward. Do not migrate any applications from the iMac to the mini — perform new installations, ideally with Apple Silicon native or Universal2 binaries (X86_64 and ARM64E) binaries. Set that iMac TM drive aside and opt for a new, fast external TM drive. I use Crucial X8 SSD which are 1050 MB/s devices using USB-C 3.2 Gen 2 cabling completely reliable over the last two years.

Using Photoshop, I consider 16GB of RAM to be a bare minimum. I was using a late 2013 27" iMac with Photoshop and Lightroom and found I needed 32GB to run smoothly with both apps open. As far as RAM, those apps are not any less memory hungry these days.

Being something of a photographer myself, I would not buy anything less that the base M2 Pro Mini. I terms of internal storage, I used to keep work in progress on internal drives but with the speed of external SSDs these days, I have moved all my data, movie, music, and photo libraries to external SSDs. I only keep what cannot be kept on an external drive on the internal. Even at that though, I would still opt for at least the 512GB as they will last longer than a 256 GB SSD since they do have limited writes and the internals are not replaceable. For this reason, I would still likely opt for a 1TB internal for longevity even though I would likely not use very much of it.

So, If I were to buy a Mini today, I would get the M2 Pro version, 1TB SSD, 32GB RAM.

You could still likely be able to get by with the M2 Mini and it would scream compared to the 2013 iMac but would suggest an M2 MacMini with 24GB RAM and 512GB SSD or if budget allows , a 1TB SSD.