info needed before looking for florist?

Hi everyone! I am ready to start my florist search and have a couple places in mind that I want to check out but exactly what info do I need before I get a quote? For example, I don't know how many guests we will have so I don't know exactly how many centerpieces we will need. What happens if I guess wrong? Also, I don't live in LI so am wondering if it's possible to call florists for price quotes over the phone or do I need to go in to get a quote?

Thanks for all the help!

When we booked our florist we just gave them a general idea of how many people we would have at the reception and how many ppl in our bridal party.

When I went we still hadn't even picked our colors (except I knew we wanted some shade of blue) so nothing is definite - we don't need to make any final decisions until like 2 months before.