[ocdtrekkie]

Ultimately, your first and foremost need is to move to a different email address: It's the hardest thing to change, it'll take you the longest. Get your own domain name, and set up an email address on that domain name. (I recommend Fastmail, but you can usually just do some rudimentary forwarding of it to your Gmail if you want too.)

Everything else you can mostly download from Google in advance, but it's key to update all of your accounts to not refer to a Gmail address. In the event of losing your Gmail address, you might lose any related account that requires access to it to verify your identity or login.

[redvenom]

I switched away from Gmail about twelve years ago. It was not hard. I did get my own domain. What I did was I started forwarding my email there. I sat down, made a list of all services that I used Gmail with and changed my address. Every time I wrote an email I made sure that Reply-to: was set to my new address.

It actually was surprisingly quick and painless.

[knaq]

Then you forget about the domain registration, or you are unable to pay due to hospitalization or finances, and you lose it.

Likewise for storage of data at home, there are floods and fires.

Reliably keeping your stuff long-term, both secure and accessible, is really really hard.

[toomuchtodo]

You can prepay up to 10 years into the future for most TLDs.

[ocdtrekkie]

As a note on this practice: Still renew it every year! It's easy to think ten years is a long time off to reach, but nine years of not doing anything and you'll have forgotten about it. And if you have lost access to something critical for renewal since then...

Renew every year, even if that date is far off.

[XCSme]

How's the email deliverability from your own email server? Or what do you use to send the emails?