After you create the bot you need to "chat" with it -> a chat_id number will be created between you and the bot;
yes, only between you and the bot -> others who will connect to the bot can't see what the bot sends (tested on 2 phones/accounts);
Yes, same on desktop and mobile on same account;
Yes, the bot token is recommended to be hidden under an apikey you can control (this is what I created for my sites: github.com/ClimenteA/telegram-push...). Not sure about multiple users for the same bot chat conversation. I didn't worked a lot on telegram bots - just enough to create what I needed. Checkout Telegram Channels.
Checkout this project: ntfy.sh/ (can do the same thing better and easier - I have not played with it yet.)
Good luck!
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No worries.
Checkout this project: ntfy.sh/ (can do the same thing better and easier - I have not played with it yet.)
Good luck!