Learn as you go
While it is true that you should look before you leap, and that attention to detail is very important when starting a business, don't put off launching your business unnecessarily.
Business theorists have often tried to identify the traits of successful entrepreneurs, and a 'bias for action' usually appears high on the list. Put simply, this is the 'Let's go for it' attitude.
At some point you have to take that deep breath and put the 'Open for Business' sign above your door. Postponing the launch longer than is necessary is not only costly to your reputation, it also delays the moment you start receiving income.
To make sure you keep your customers happy plan to be able to deal quickly and efficiently with any teething problems that occur.
It is a curious fact that businesses that deal effectively with customer problems have a higher customer loyalty rating than those businesses that never seem to have any such problems.
Set a realistic start date, stick to it, solve customer problems as they arise, and never look back.