Writing this on GrapheneOS right now:

• I think esims remain on your device, but I’m not 100% sure. Most providers allow you to, fairly easily, request a new esim though, just make sure you go through necessary verification steps before you switch -You can install Google Play, it’s just not pre installed. I unfortunately have a few Apps that don’t have a FOSS replacement, so I just have those running as normal
• Yup, I have my Google account set up as I would have on any other android phone, with Gmail, google messages, … all working as expected
• If you had them synced to your Google account through individual apps in the past, they’ll be synced here too. Just be aware that Stock Android full OS backups can’t be restored on GrapheneOS. Worst case, there are apps that’ll backup your messages and calls to a file, and you can simply copy that off your phone, and put it back on again after the conversion
• If they’re saved in Chrome, they should also sync over. But as others have mentioned, you can also just get a proper password manager like bitwarden and have them in there. That’s what I did, and I don’t regret it. And yes, they’ll still autofill in apps and stuff
• That depends entirely on your bank. If your bank issues its own cards through its own app, they’ll most likely work, see the list other people have posted. If your bank relies on Google Pay, it won’t work.

I think that should answer everything? The installation itself is super easy and painless, their online installer works like a charm, so in that regard it’s probably the easiest custom tom I’ve ever installed