Haven’t dived that deep yet, but who knows. Maybe I’ll get there eventually. I’ve heard good things about this book: https://www.tiltedwindmillpress.com/product/ryoms/
You also don’t need to do everything all at once. You can start by getting your own domain and configuring your mail service of choice to handle it. Then whenever you want to move to a different mail service or run your own, you maintain control over your addresses and just need to update your DNS.
Edit: Oh, completely forgot to talk about Proton/Tuta. I set up my stuff on Proton back in the day and recently set up Tuta for my partner. I might get around to swapping to Tuta for my stuff as well, I just haven’t bothered to yet.
There’s a whole section for controversies: https://en.wikipedia.org/wiki/Proton_Mail