I agree with the backdoor risks, that’s why I don’t recommend it for safe communication, I know that Telegram is partially open source now, but I can’t remember if it applies to the encryption

Yes I do use a VPN, 24h 7/7, changing server everyday. regarding their data collection, it’s about the same as WhatsApp for exemple, the difference is in which government will they comply with, if you are american for example, you better have your data in russia with Telegram

Yes they have your phone number but you can easily rent an anonymous number to use services that require it, and even then, if you do not plan to become a gun dealer, you just set a username and hide your phone number everything will be okay (again, for the social media use case)