The other benefit of getting an extension instead of overstaying by one day is you could be stopped by the police on the way to the airport, then jailed, then deported. The odds of being stopped are very low but not zero. The consequences are very high.
It’s difficult to work in Thailand and stay longterm unless you’re 50 years old or older. Lots of information on the Thai Embassy website for your country and on Google. When you are serious about starting a company or buying into one, legal advice is definitely recommended. Everyone talks about how nice the Thai people are and they are in general. However, there are also Thais that take advantage of foreigners. You need to protect yourself from them.