, I am doing the same as a registered business owner in Australia. I prepared a letter stating that my role within the company was eligible for remote work.
I had 500,000 Baht in the account a matter of hours when I sent my application in. This was in Australia back in December. It was accepted following a request for some additional documents not related to the bank balance.
The DTV Visa is activated upon acceptance by the consulate you apply through.  Given the period of time for processing being on average 6 to 8 days I would be doing the application about 2-3 weeks prior to your requirement for it as to not waste a month or two of the Visa period.
Yes get a PDF creator app and create one document. You may need to make it black and white to reduce the file size. From memory they can not be larger than 3MB. As mentioned above wait to hear from them now. I called the Thai embassy to discuss my application in Aust and my supporting documents. They were very helpful. My application was approved. 24 hours later.