I'd be fine with tags in the digiKam DB including all of the above, but the values written to the images IPTC keywords field would have to be limited to the subkeys of what you listed above as type and content hierarchies. Here's an example of one of my images: https://www.flickr.com/photos/tcgoetz/53265234720 you can see what I use for keywords in the info below the image.
My workflow also includes grouping similar images, using compare to grade them best to worst, marking the best with the pick flag, and rejecting the worst. I also group subimages of panoramics with the generated panoramic as the top of the stack and the pick image. didKam has a group feature but it seems different. Grouping in LR hides members of the group other than the pick image.
For sure. I don't doubt it will be a faster machine. Most of my issue are about the costs for the incremental upgrades. The base machines all come with to little memory and ssd. The upgrades cost way too much for what you're getting. My high end 2019 macbook pro cost ~ $2500. A high end macbook pro now cost ~ $4000. I would expect the new machine to last for four years like the last one did. I have a 1TB ssd now. It's 3/4 full. The biggest consumer of space is my primary photo catalog. If I upgrade my camera in the next four years the megapixels will probably double and space will fill up even faster. The upgrade from a 1TB ssd to a 2TB ssd is $400. That's way out of line with ssd costs anywhere else. And yes, I only keep my primary data on the laptop and push everything else of to my NAS.