Who said you shouldn’t be able to access your backups remotely?
A lot of tools allow you to set up google drive, drop box, whatever. Yes, this brings you back to cloud, but it’s better to have a hacker wonder if some random google drive might have juicy auth data than know for sure that some SaaS platform absolutely does. Also, even if they got the file, it should be encrypted, and should be a massive pain to get into (at least long enough to change the passwords stored in the file).
The other (better) option is to have it back up to sftp (or similar), which you manage yourself on private servers. Normally this would be accessed through RSA and/or TOTP, but you can set up secure backup methods (combo any/all of; port knocking, long-password, human-knowable timed password, biometrics, security questions, other trusted humans that have some TOTP that can’t open your storage alone, etc).
Whoa there, I never have - and never would - suggest that anything should be protected by a single factor. Where are you getting that?
Authy sucks. It’s not just that the TOTP they send you might not be secure (SMS is easily exploited), it’s been shown that they’re leaking other personal data.
You don’t have to cobble anything together. As you say, self-hosted BitWarden is a good option. As for your “glue”, you should trust it more than a third party, since you know what went into yours, and its not a massive
honeypottreasure trove.Edit: I’ve been using “honeypot” wrong. It would actually be good if the hackers tried to hack one of those.