If you’re looking for more tinkering on the music around the house front, Lyrion music server + squeezelite players can be a very fun endeavor. I think it gets a little sketchy if you’re favoring automation and casting, but as a network of players that will utilize a wide swath of hardware, it shines. I had a bunch of pi4s laying around and eventually repurposed them all into a multiroom audio gang.
Startmail (from the Startpage folks) has been fine for me. You pay for it, you can put your domain on it, you can do alias addresses, works with any IMAP client since it’s just IMAP ran by a (so far) competent company. Their web ui is fine, but ive only used it for initial setup. Besides Thunderbird on mobile I use Snappymail within Nextcloud and this works just fine as well. All I can say is it does what it says on the tin.
I did a 4 node Pi4 kubernetes cluster for about 5 years. The learning experience was priceless. I think most notable was learning to do proper multiarch container builds to support arm and x86_64. That being said, about half a year ago I decided to try condensing it all into two n100 nuc-like clones and keep one pi as the controller. For me and my apps and use cases there was no going back. Performance gains were substantial and in this regard I think I was hobbling myself after the educational aspect plateaued.
Tidal has been pretty good for me over the past 5 years. I don’t know what your criteria are, but for me it’s something like 1) is the catalog big enough to offer 90% of what I’m looking for and 2) no advertising if I’m paying for the service. It ticks those boxes. I imagine it’s only a matter of time until they introduce the bullshit tier where you’re paying and being advertised to, but for now you get what you pay for.
The Earthsea books play heavily on both born in attributes and acquired skills, and I’d even say the interplay between those two concepts. Really great books for youth and adults.