Advice needed iMac 2012 with Lightroom 5, 3 huge catalogues 3K pics

Assuming you have purchase the Adobe Photography Plan (not the Lightroom Plan) and you are using Lightroom Classic:

Answer to question 1: It probably means that this is an UPGRADED catalog, and to distinguish it from the previous non-upgraded catalog, the name was changed by appending -2 to the filename. I would use the most recent catalog, although that's not a guarantee either.

Answer to question 2: With Lightroom Classic, you are not able to backup anything to the cloud. If you are using Lightroom (not Classic) then your photos are automatically backed up to the cloud.

Side question: why purchase the 1TB (not 1GB) plan if you're not going to use that space; you should purchase/subscribe to the 20GB plan and save $10 US a month.

https://www.adobe.com/creativecloud/photography/compare-plans.html

I assume that the Tb plan will not be enough.

By @Rictor133

If you are really talking about Lightroom Classic and you say “Tb plan” referring to the Adobe cloud storage plans, then it needs to be said that you don’t have to increase the size of Creative Cloud storage for Lightroom Classic alone, for a few reasons. One is that because Classic only stores originals locally, nothing gets synced to the cloud except for specific images and collections that you enable sync for. Another is that if you do sync some images and collections, only Smart Previews (raw capable proxies) are synced to the cloud. And finally, Smart Previews don’t count against your Creative Cloud plan storage limit.

The reason to upgrade Creative Cloud storage to 1TB is that you intend to make full use of cloud storage, like you are going all-in on cloud Lightroom (not Lightroom Classic), or you are going to upload lots of Photoshop Cloud Documents (PSDC files) instead of the traditional local PSD files, or you are going to open Photoshop and stuff Creative Cloud Libraries full of images. Or maybe you plan to use the Lightroom cloud apps (for desktop, phone, or tablet) to upload up to 1TB of originals that will later be downloaded by Lightroom Classic.

But just for Lightroom Classic alone, the lowest cloud storage level is usually fine.

I am going to wait for the M3 Mac mini and will go with 16 gb ram, and 512 internal storage and use mainly ssd hard drives, apple internal storage is crazy expensive.

By @Rictor133

Sounds like a good plan. Many of us do the same thing to save money, there is zero downside to keeping images on external volumes for Lightroom Classic. I do want to mention that although 16GB of unified memory is OK, people are starting to think of it as the new minimum, and 32GB* will probably be a better choice in the long run. Part of it is because apps like Lightroom Classic are using the GPU more (for graphics acceleration and new AI features), and the Apple Silicon GPU gets its graphics memory from unified memory. Having more than 16GB of unified memory makes it more likely that there is enough to distribute among macOS, the apps it’s running, and the GPU. 16GB makes it more likely that there will be a bottleneck.

*Some new M3 Macs offer 8/16/24 or 18/36GB instead of the old 8/16/32GB, and we don’t yet know how Apple will set up the M3 Mac mini when it gets here. If the M3 Mac mini maximum turns out to be 24GB or 36GB, I would pick either of those over 16GB.

On a side note, your original post mentioned using Affinity. I noticed that a press release just went out this week that Affinity has been acquired by Canva.