Not only is that not harebrained, I think that is likely the primary reason. I experienced some transitional pain too. You have to tell yourself to take it easy and don't push yourself too hard. Once you've made the decision to switch, it's tempting to want to do it as quickly as possible, but doing so will put extra strain on your hands and fingers as they won't have the muscle memory yet for the new set of movement patterns.

The piano thing might be a factor too, but that's outside my experience.

I experienced very high levels of fatigue after my second day of using Colemak for actual work. I fortunately don't get pain from typing, but they would shake if I held them out in the typing position.

That was the day that I had a huge boost of speed to the point where I could reasonably compose emails and chat messages without needing to revert to QWERTY, so I was naturally getting more mileage, but I compounded that by also doing more typing test/training than ever before, because I was so motivated by my performance jump.

The big problem, other than the sheer volume of typing, was that my mental accuracy was still far too low to safely drive my typing as fast as I was trying to push. This meant that, even when I didn't technically make an error, I was only saved by my fingers making a sudden correction at the last second. In terms of hand fatigue, I think this was actually worse than if I had simply made the errors but maintained natural finger motions (i.e. confidently failed).

The next day, I made an effort to slow down sufficiently that my fingers moved smoothly and decisively. This allowed them to physically recover nicely. I'm also hopeful that it helps build more accurate muscle memory. I can certainly say that the 'B' key feels so much closer now that I'm not juking down towards its old QWERTY location every time.

You shouldn't try to minimize pinky usage, that's a common beginner mistake. Pinkies shouldn't have same-finger bigrams or lots of row jumping but they need to work a little for their living to make a really good layout. QWERTY users often have notoriously useless right hand pinkies due to underuse, but this is remedied with a little training. Don't fall into the BEAKL trap and make a substandard layout just because you have untrained pinkies! Colemak has decent pinky usage and low pinky travel, as it should.

Layouts like Halmak (and Workman and Norman and...) will try to draw you in with a lot of bragging. Most of them aren't all that much, really. Halmak isn't considered that good anymore. ISRT, sure, that's a good layout but it has little support and its maker NotGate/Whorf seems to have moved on to other ideas. Apsu is making good layouts these days, and Apt looks promising... but it isn't out of beta-testing yet and keeps changing. The cutting edge of layout design is very much a bleeding edge, with lots of promising ideas and extremely uncertain benefits. Some ideas there are interesting, such as a guardedness against redirects/pinballing (rolls that change direction) which wasn't really considered a decade ago ttbomk.

Since you confess to being prone to rabbit-holing (and bike shedding?) I hesitate to point you in the direction of good alt layout resources. I really can recommend Colemak(-DH) with all my heart! And with it it's easy to go further, adding tools like Extend and Compose (using the EPKL program for Windows) to become very powerful. Instead of fussing over layout choices, research such tools as described in the BigBag and other places. They'll provide a lot more utility than over-optimizing your letter positions beyond Colemak will – I can guarantee you that!

EPKL will also help you write fancy symbols and Greek letters and boilerplate text and whatnot, through dead key and Compose and Extend layers.

My personal opinion on pinky usage is that they are perfectly fine to use for tapping on the home row or directly below the home row, passable for tapping directly to the side or one down and to the side, and awful for anything above the home row. The real problem for the pinkies is chording <Shift>. The proper solution to overworked pinkies is moving <Shift> to a thumb.

The atreus certainly doesn't put too much strain on the pinkies as each hand is only five keys wide, so its physically impossible to stretch the pinkies to reach a key, stretch a pinkie and it just falls off the end of the keyboard!

Forces you to use your thumbs for all the modifiers/layer keys.

No emacs pinkie with this bit of kit..