re: How is the order of stimulus direct deposits determined?

Most recent update from IRS.gov yesterday was 3 weeks before they get them started. Details are getting worked out along the way. I'm guessing here but I expect several different areas to process checks or direct deposits so it's hard to say how they will do it.
If you are a senior or disabled and haven't filed a tax return in a while you will need to file a simple 1 page "tax return" to get your money (just basic info & directo deposit info). Go to IRS.gov, they're pretty good at having updated information.
SBA forms should be available sometime Friday.
Stay safe and wishing you good health.