When you accept a new job, you don't know who you are going to work with, what you are going to be doing, and how much (or little) you're going to like it. Call everyone you want. Ask their opinions. Trust the fact that a good friend referred you for the gig. Revel in the idea that the company has a good pedigree, but don't delude yourself that in a smattering of interview hours you're going to have anything more than a vague hint of your new life.
Try this. Tell me about your best friend. Give me a bulleted list of five noteworthy things you think I should know about your best friend. Got it? Read it out loud. Does this do justice to your best friend? I hear you when you say, "He'd do anything for me," but why is that? ...