* Use your own domain, but don't use Google Domains as the registrar. If Google locks you out, you use everything.
* Don't use Gmail as the admin account of your domain registrar. If Google locks you out, you lose everything. But don't use your own domain email as the admin account of your domain either. It's ok to forward to your Gmail account, as long as you can access the other email account when Google locks you out.
* Don't use Gmail as the contact address of your credit card on your domain registrar. If Google locks you out, you will miss notifications of payment problems.
* Backup your Gmail, Google Drive, Photos, Calendar, Contacts, etc. to somewhere else. I recently purchased a Microsoft 365 account for this purpose, $70/year for 1 TB of storage. Ironically Google is making me spend money on other providers because of Google's complete lack of customer support and their rapidly degrading level of trust.