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

Ah, but you see, if you wrap it in Saran wrap, they won’t be able to make contact. You’d be better off using contact grease for that easy insertion

Well, they say they’re studying at a university in Slovenia, which gives it a pretty good chance that English isn’t their native language. Those questions still get across what they’re asking, so unless you’re some kind of grammatical god, I don’t think you can really complain too much

I was in your shoes a few years ago, so I think I can give at least some insights: Regarding VPNs, Tailscale is based on Wireguard, but makes configuration a whole lot easier, especially if you have devices with changing addresses. You do still need an account with them, but from there you simply install tailscale on every device you want to access via your VPN, and they should automatically get assigned IP addresses (100.x.x.x). Entering this assigned IP from any other device connected to your Tailscale network will give you a direct connection between the two. With a bit of fiddling you can also enable subnet forwarding, allowing you to for example connect to devices on your home network that don’t support installing software on them, but at least for your current setup I don’t think that’s necessary. It is fun to play around with though, and opens up a whole new world of possibilities. I use it to remotely manage my parent’s Router for example, since merlin-wrt and many managed switches don’t easily support additional software.

Cloudflare Tunnels are Kind of similar to a VPN, only that you don’t connect your own devices with eachother, but instead connect your server(s) directly to cloudflare, who then take over the task of actually getting your data on the internet. The advantage of this is that you technically don’t even need a public IP address, since any requests and answers will be forwarded through the “VPN”, and only cloudflare needs to be publically accessible. This does require you to buy a Domain though, since that is what the forwarding will be based on. In the same vein, but if you want to do things “more manually”, I’d also recommend you look into Reverse proxying, if you haven’t already. That’s basically what turns “site1.example.com” and “site2.example.com” into different requests, usually to different IPs and/or Ports on your private network, allowing you to have multiple things running under one domain. Personally I use the “Nginx Proxy Manager” running in a Docker Container for this, mainly because it’s nice and easy to get your head around, but there are several newer Options like Traefik or Caddy that I also want to look into at some point.

After this wall of text, I hope you have fun playing around with all of this stuff, I know I had, and I really learned a lot about networks and the internet in general. Oh, and don’t be too stubborn to completely start from scratch occasionally, sometimes it’s just the easiest solution…