How much money is required upon arrival in Bangkok with visa exemption, and what are my options for obtaining a non-B visa for work?

I’ve done several searches online and in this Facebook group regarding how much money you need after arriving at BKK, but can’t find a definitive answer. (Ill be entering w/ visa exemption) Is it 20,000 baht or 10,000 baht per individual?

Additionally, I have to apply for a non b visa at KL or somewhere else so that afterwards I can apply for get a work visa and extension for my teaching job that starts August 1. The only proof of departure I have is a flight out of the country on October 1. Will I need to purchase an additional departure flight within the 30 day visa exempt period and avoid discussing my work contract since I do not yet have the permit?