Does my eSIM remain intact on the device?

Define “intact”?

How do I get apps without Google Play?

Aurora Store, Drodify, Accrescent, Obtainium, etc.

Can I still attach a Gmail account for notifications without going all in?

If your admin settings allow you yo use a third party app, yes.

What about contacts and message history?

What about them?

Is there a good way to get my password keychain transferred?

I dunno what a “password keychain” is.

What is the status of NFC payments?

Can’t do it. Carry a credit card.