> 2. Like Whatsapp, server has to store the message until the receiver is online again (until they open the app).
The server actually has to store it for a maximum of 30 days [0]. Snaps get deleted after 30 days (even if they're unopened). They're deleted immediately once the Snapchat servers get confirmation they've been viewed.
Sure, why not? They might work with the FBI to store data for specific targets, and the NSA probably intercepts and copies a lot of data onto their own servers, but I see no reason why the company itself would lie about this. They probably do delete the data immediately for the vast majority of their users.
2. Like Whatsapp, server has to store the message until the receiver is online again (until they open the app).
3. Whatever systems they use for advertising, tracking, profiling, and analytics is probably a significant chunk of their backend.