"Artists Beware"

I just have some question to ask. Noting serious here.

I decide I want to bulk order art from an artist but bulk ordering seem more dangerous and hard to me.

So I just want advice on bulk ordering since I never done it before.
I need advice on both type of bulk order:
-the one where you paid for all of it at once
-the one where you pay for each

Also any tip on how to order bulk order like is there a special format I must follow.

Thank in advance for the advice.