I can only comment on the first paragraph. You don't need proof of flight. As for the accommodations, I booked a hotel first that is fully refundable and used that. After DTV is approved, you can change that hotel booking as you're not committed to it.
It's best to have at least 500,000 baht over the course of 3-6 months. My understanding behind the reason for this is to demonstrate that your monetary balance was not injected last minute to give the impression of financial stability, which would defeat the purpose of this requirement. That said, I would think that the strictness of this rule varies by country and embassy
someone else said maybe it's because my flight date of Oct 16 is far enough away to not be prioritized. May I ask roughly what date you set as your flight/arrival date?