“with great zeal” 
… expectation management in marketing copy is hard. I’d return to Google Android on the main phone and explore /e/OS on a secondary over a longer time. While a lot of Google products will work, if you’re strapped on time and use it in a business function it invites frustration. You want everything to work at once - it won’t.
One thing that eases a migration away from Google is diversification in the tethered products you use - as in not Google.
- Password sync Google Chrome ↔ Murena web passwords ↔ Cromite (in-built Chrome fork) on the device: that functionality isn’t there. The help page explains how to do one-time imports - but no sync. You’ll need more software on the device to sync from murena-web-passwords and provide the Auto-Fill service in Android. Unsure why it isn’t yet packaged in /e/OS that way. You could be better of with another 3rd party pw manager: Bitwarden, Proton, Brave / Firefox Sync even
- Google Calendar: those of your own Google user that you added through Settings → Accounts will be available - adding another users needs an ical link
- it was 404’d because apparently the webapp couldn’t be authorized again - that blame isn’t really on Murena imo as Google required probably an app audit. That intro Email needs updating
- unsure if Whatsapp backup restore from Google Drive works. Transferring the old directory will. On the migration page is a link to a 2020 forum entry that I think still applies - Migrate to /e/OS
- Gmail should work through default Mail app after having added a Google Acount through settings (as should event or addresses in the default calendar and contact app). If it doesn’t it’s considered a bug - even when you use 2 Google Accounts
I get you started to use Google apps out of desparation and run into microG complaining about “account already added”? not sure how many users are around to know to what extent this works, I’d start a separate thread for it