Learn Spanish (Spain): La pastelería está a punto de abrir.

The phrase estar a punto de followed by an infinitive (like abrir) means to be about to do something. It is a very common expression used to talk about things happening in the immediate future.

Why does the sentence use está instead of es?

Because it is part of the fixed phrase estar a punto de. Even if you think of an opening time as a scheduled event, this specific expression always uses estar to describe a temporary state right at this exact moment.

Since the shop isn't opening a door or a box, shouldn't it be the reflexive abrirse?

You do not need the reflexive here. When talking about businesses starting or ending their daily operations, Spanish usually just uses the normal, non-reflexive verbs abrir (to open) and cerrar (to close).

Is there a pattern to the -ería ending on pastelería?

Yes! The suffix -ería is commonly added to a word to describe the shop that sells that item. Since pastel means cake or pastry, a pastelería is a cake shop. Other common examples are panadería (bakery) and carnicería (butcher shop).