What is the best way to start your own pastry from scratch?

Before you even get into the business thing, find something to make yourself unique. try out special recipes, make them your own, ect.

Then start selling at local markets

(most towns have them at least once a month) and get a bit of a name for yourself. with purchases hand out cards with your business details that says you can do cakes for events and stuff. if you're really good at cake decorating go a little mad with it and you'll get a name for yourself, but don't go ace of cakes style and do only specialty cakes unless you're just THAT awesome.

by the time you have a pretty good rep and have earned enough that a small business loan wont worry you too much, opening an actual store will be a breeze. As you would have already built up your rep getting the customers to maintain a shop will be easy, specially if you keep doing the local markets and other such events.