Questions on using customs brokers

I know I want to employ a customs broker, but I have a few questions about that. What all do I need to have ready when I contact one? I have a business license and state tax ID, a domain name and the barest beginnings of a web site. And can I tell them what I want to import and the broker find the sources or do I need to provide them with sources? Do I need to be a going concern business-wise or will they deal with someone who is just starting up? And any other info anyone can share would be welcome, I'm sure there are other questions I should ask that I haven't thought of yet.

Thanks in advance.

-Sonja