Alright so after checking logs, rebooting the vps because why not, and removing and re-adding the account in thunderbird... Now nothing is working other than sending mail from gmail to the domain. imap does not pick up the email and trying to send with the domain just plain fails, saying it can't connect to the server.
Honestly, tempted to uninstall dovecot, sasl and postfix and start again, but I don't want to run into the same issues with conflicting tutorials. Does anyone know of a good source of how to do this that's fairly recent? I'll keep searching, but all of the outdated info is kind of frustrating.
If anyone has replied to me I haven't gotten it yet, so I'm not ignoring anything you may have said. For now going to give this a break. I've been working on it literally all day! :)