b) telegram is not end-to-end encrypted by default. And not end-to-end encrypted at all for group chats. That's kind of a dealbreaker. Telegram is one of the last messaging apps I'd recommend.
In my country whatsapp messenger can and will be seen by the government if there is a request. Have heard it many times.
I don't think any messenger or anything you write is actually secure or actually private. We just came to terms with that.