I took 8-9 months off a few years ago. I absolutely recommend it, especially if you feel like you need it. I didn't travel much, other than to see friends elsewhere in the U.S., but I didn't get bored. The highlights were training for and running a half marathon, improving my cooking, developing habits for keeping my apartment clean, reading lots of books that had been sitting around, and random fun coding things like Project Euler. Not having to keep to a set schedule was liberating and wonderful.
It wasn't more expensive. I was paying for a COBRA health plan but I was eating out a lot less, and it mostly balanced out. Apart from securing health care, there wasn't anything I would have found useful to plan ahead of time. I do wish I had traveled to Europe or Asia, but that's my only regret. It's all "you time" and you can just trust yourself to know what you want to do once you go through the initial recovery from the stress of working. For me, after about seven months I realized I was ready to go back to work, and I was lucky enough to find a job that I've been at since then. I will likely take another extended break, but maybe just 4-5 months, and I will be sure to travel then.
I'm currently working through Naive Lie Theory https://www.amazon.com/Naive-Theory-Undergraduate-Texts-Math... by Stillwell and there's a lot about quaternions in the first chapter, including their standard matrix representation. You'd need to be familiar with some group theory to fully understand the 3D rotations but the matrix operations are clear enough to start coding with, I think.
The two negatives were PCR tests. Those are different from antigen tests. The blog post you've linked says there is a problem with false positives with PCR tests, but that doesn't seem to be relevant here, given that both of those results are negative.
It wasn't more expensive. I was paying for a COBRA health plan but I was eating out a lot less, and it mostly balanced out. Apart from securing health care, there wasn't anything I would have found useful to plan ahead of time. I do wish I had traveled to Europe or Asia, but that's my only regret. It's all "you time" and you can just trust yourself to know what you want to do once you go through the initial recovery from the stress of working. For me, after about seven months I realized I was ready to go back to work, and I was lucky enough to find a job that I've been at since then. I will likely take another extended break, but maybe just 4-5 months, and I will be sure to travel then.