1/ yes you shouldn't apply more than 3 months before your intended flight date. However, having said that you could say your intend to fly in May (for example). Find flight number for said date and then once approved they don't care when you choose to enter Thailand people's plans change all the time. The visa is for 5 years so come whenever you want.

2/ you need bank statements. More and more embassies are asking for 6 months of bank statements. The most recent one needs to be at least 500k

3/ proof of current location can be your driver licence

5/ no need to upload flight details. For accommodation a lot of people are booking fully refundable thai hotels on agoda etc. Then cancelling it after being approved