My guide always answers emails in a timely manner, and will discuss anything that I want to, including add-ons, via email. I think each one is different in how they do their jobs. Definitely after 1 week with no response, I would re-send the original email, with a note saying something like, "You must not have received this, since I didn't hear back from you, so I thought I'd better send it again"....that way, you sound like you're giving him the benefit of the doubt, that he didn't get the email, but it will give him a kick in the butt, if he did.