There's no income requirement for the DTV. But yes, your business must be registered and you should have a separate bank account.
Most places don't accept retirement or investment accounts to meet the 500k baht requirement. So put that money in a savings or checking account unless you already have 500k in checking or savings. How long it needs to be in there varies by where you apply. Hopefully, someone with more specific knowledge of Chicago can chime in.
To extend a non-O, you must again show that you meet the requirements, including financial. I would assume the same with extending the DTV, in the country. But with Thailand, you never know :-)
it's possible to extend this visa while in Thailand, you'll need to again show 500k. We don't know yet. Or, you'll need to leave the country and come back
At a minimum, with the DTV, you'll need to leave the country every year. That will eat into any profit you make by having money earn interest.
Plus, the non O for retirement doesn't require you keep any money in the bank. You can meet the requirements by bringing in 65k/month, or for some folks, showing documents that you earn that much.
IMO, DTV makes sense if you regularly travel out of Thailand. If you don't, non immi O for retirement purposes might be better.
To anyone who is 'not bothered' by air pollution, just because you're not experiencing noticeable symptoms right now doesn't mean you're in the clear. Air pollution is a risk factor for heart disease and dementia, as well as the obvious. I wouldn't worry much short term, but if you're going to stay a while, consider it.