Bring 6 months of statements but the 500,000 baht or equivalent doesn’t need to be in your account for all 6 months. At least that was the experience of the people I know who got it. I have my appointment next week so I can let you know more after that. You should get an appointment first. Slots open for the next 2 weeks but fill up quite quickly.
I’m in HR. The employment certificate should be on your company letter head and have your name, passport number, job title, company name, current salary, length of employment, and that you can work remotely. Should be signed by HR and have their contact info and should also have a recent date.