What should I consider when submitting flight documents with my DTV application?

So I’ve been asked to provide flight documents to attach to my DTV application.

I’m hesitant to do so because there’s no guarantee my application will be approved, and I may want to travel a month or so later than the date I originally mentioned.

A few questions:

1. What’s the risk if I arrive a few weeks or even a month later than the date stated in my application? Will this cause any issues with approval or entry?

2. Why isn’t the flight number I found for the same date which I included in the application form not sufficient?

3. Has anyone else received this request before, and how did you handle it if your travel dates weren’t confirmed yet?

4. Do I need to book a return flight?

Thanks in advance for any advice or experiences.