For what it's worth, I use Fastmail + a custom domain and couldn't be happier. But I'd hardly recommend it to everyone for personal email.
I'd recommend for #2 picking a date that you do other annual preventative stuff on, such as changing your smoke detector batteries. That way you build an association in your mind between that other stuff and extending the domain, making it further unlikely that you will forget.
Generally, you can start out with 10 years. Some registrars offer even more, but the underlying registries generally only support 10 years. The registrars that offer more do so by doing 10 years with the underlying registry and then automatically extending that every year transparently to you. If they go out of business more than 10 years before the end of the term they purported to sell you, those remaining years will go poof.
Also have on your calendar reminder for #3 a reminder to check to make sure your contact information still works, particularly email. If you own domain X and use it for email, you probably don't want to use an @X email address as your contact address for the registrar you registered X from. If something goes wrong with your account or domain at the registry and they try to contact you, you don't want their email to you to get eaten by whatever problem they are trying to contact you about.
And 2FA? Yeah, if you’re not already doing that for PayPal, Venmo, eBay, and others, you’re not gonna add it for your domain. If you are already doing that, it’s no extra burden.
They've just been super reliable and mature for me. No huge updates that force me to adjust. Interface is nice and clean, uptime and service super reliable. Everything just seems to work for me (aliases, forwarding, filters, good Android app), and the pricing is within reason.
I actually use their web interface and official Android app. I'm surely no power user, but have used various providers over the years until I settled with Fastmail (seemingly for good). It's difficult to decide whom to trust with e-mail but to me they seem trustworthy. I still like to have my own domain, so I could in theory take it with me, if I ever started being displeased.
In general: Paying for a service (especially e-mail) is invaluable (my data not being mined), also for potential account recovery (didn't use their customer service often, but when it happened, it was decent).
I can't comment on ProtonMail but especially with e-mail, a proven (long term) track record is gold, and Fastmail has it.
addendum: upon rereading it almost sounds like a Fastmail commercial. I'm only a satisfied user without any further connection towards the company.
At the time when I evaluated, FastMail just worked, and their standard support remains excellent. IMAP works great. The ProtonMail bridge thing put me off to be honest. There's not too much else to it.
Either way though, both were preferable to Gmail, which I wanted to drop along with all Google stuff if I could. And being lazy/just wanting it to work, I chose Fastmail.
Between those two, proper IMAP support (including IMAP push) is the big thing. Webmail generally drives me nuts for anything beyond stopgap usage, and while ProtonMail has a local IMAP adapter thing it’s a step too involved for me.
IMAP support is incidentally also why I don’t use Gmail. Their IMAP implementation is spotty and notoriously bad with Apple Mail, whereas the experience with FastMail is flawless.
I left migadu because they repeatedly demonstrated they were neither professional nor reliable enough to host my email (that is bargain basement pricing for you). I looked around and trialled several services on my other domains; I settled on fastmail as they had a proven track record with recommendations from people I trust who know email, every feature I wanted, and decent pricing.