Your accommodation is very important and usually, it is stated in your sponsor letter.
But embassy may or may not ask your hotel reservation if your ex husband cannot accommodate you(as you said). Flight bookings is I think a requirement because I showed my bookings when I done my application. Some applicants paid their bookings and they wasted money for that because they paid their ticket already. But some airlines only accepts booking fees. That means, you only need to pay your booking, not the ticket. You also need to pay your travel insurance and that is really a requirement. The cost is depend upon the insurance company and how much requirement you need to be insured. I paid around P 9,000 for myself five years ago.