mautrix/telegram is a bridge between Matrix and Telegram. It mostly lets users of Matrix contact their friends who use Telegram. It is not a fork of Telegram and has nothing to do with the Telegram interface. (Note: OP wanted to use the Telegram client with a non-Telegram server. If you know of a Matrix client which looks and feels like the Telegram client, thats what theyre after.)
Im not sure how difficult it is to setup a Tailscale client, honestly.
The Zerotier setup is just installing and joining a network by an id. The Windows version has a bit of a GUI, where you have to right-click on a status bar icon, click Join network, paste in the id and join. The Linux version of the client has a cli, which is imho even better, as you can just send them a whole command to copy into the terminal.
I admin a Zerotier network for a bunch of kids that wanna play Minecraft, and they havent had many problems setting up.
There is a bunch of information on self-hosting the whole system, but Ive honestly never tried any of that. It was just nice that this was “just the open-source LogMeIn Hamachi with a superior implementation of everything”.
I see why automatically giving them out (like in ACME) would be a bad idea, but other than that, why not? Even https://1.1.1.1 has a DigiCert cert.