How to use purchase orders module in the right way?

How to use purchase orders module in the right way?

Let's say my boss tells me to order 70.000 Black T-shirts and look for a company which can supply them.

Taking into account I have to search for a supplier and of course I do not know the pricing. Should I enter the information to Zoho Books and create a purchase order for unknown supplier, or wait until I have confirmed with supplier and then create the purchase order?