Plot questions in Dracula

I can't figure out how Dracula controls Lucy and Renfield before he even sets out from Varna in Russia. How does he even know of their existence? I can just imagine that Jonathan somehow lets slip the name of his fiancee's best friend, but how would he even know of Renfield's existence, let alone be able to control him from a couple of thousand miles away? I'm assuming, of course, that the Lucy's sleepwalking and Renfield's fly- and spider-eating are somehow the result of Dracula's influence?

And while we're at it, what's Renfield for, anyway? As far as I can tell, he doesn't play any part in the plot, although he does commune directly with Dracula when he escapes from the asylum to Carfax.

Well Renfield was the solicitor originally sent to Dracula's castle to sort out the Count;s affairs but then was driven insane. He was then committed to Dr.Seward's Asylum and Jonathan was sent to the Count's castle. So that's why he has the control over Renfield. As for Lucy, I believe that she did have a problem with sleep walking before Dracula. But since Dracula can transform into many different animals such as wolves an bats...etc. I think this is how he led her to him and she originally came under his power. Of course, this is just my opinion :)