Budget, Date and Amount of Guests
These are three things that you need to have present and resolve before you call, or visit any vendors, or venues.
If you are paying everything define how much you are able to use, the percentage of each thing you need for the wedding
If you will have other people helping with expenses please, always ask the amount so you can added up and have that present for you to be able to call or visit any vendors. Other information that you need to know are the date and amount of guests. That way the vendors will be able to give you a quote.
If you don't know the budget and amount of guest you won't be able to look for the proper venue. Every vendor needs these information.