'Open and Ready' does not mean it is receiving income. It is READY for income (customers have the opportunity to come to you and pay you, even if nobody actually hires you). So if customers/clients were able to come to you in September, that is when the business started. If you were just doing preliminary work for the business but not available for customers/clients until a later date, you use that later date.
No, you can claim any valid deductions, including Startup Costs, if your business is open. There is not a requirement for there to be income.
