The bank account question has been answered a lot of times. Since you can’t apply for this visa in Thailand, it is clear that they don’t expect you to have the funds in a Thai bank account. Since it is a glorified tourist visa, you can’t really even open a Thai bank account in many instances (people find ways around though). You have to prove your employment. If not employed by an employee, you need to show evidence (portfolio, payment slips, tax receipts, etc. they vary by embassy).
you can also be a freelancer, but seem to need to show evidence like tax returns and letters from those who receive your freelance services. That is at least what many others have said