Search for requirements from the specific Embassy you want to apply at, since the requirements differ quite a lot.
For DTV the 500.000+ Baht deposit can be in any bank anywhere, and you will have big difficulties with opening a Thai Bankaccount,both with and without DTV, so don’t count on that being possible.
Most Embassies recommend that you don’t apply for any visa, more than 3 months before arriving in Thailand, as can be read at the website of the Thai Embassy you will apply at.
There are also a lot of other important information on that website, you need to familiarize yourself with.