How to handle lots of site traffic [View all]

I've created websites for years, but never released one of my own to the public before, and now I might actually start marketing the one I'm about to finish, in a couple months.

How do you prepare for a lot of traffic? I'm not concerned about data usage, since unlimited is pretty common, but about speed. Now I'm using a $6/mo GoDaddy account, so as far as I know, it will get bogged down after a second user logs in. Would it be beneficial to use a second service provider, like Media Temple, to serve up the images separately? I was thinking mediatemple might be better than godaddy for image repository, since my site will have lots of them, and they specialize in that sort of thing.

I know this might be a pipe dream, but say I had 1,000 visitors a day, or 10,000? What would I need. How many servers. How many T1s? I know it is a factor of the processing the website does, but say for an average site like an ecommerce site, or this one. Surprisingly when I called GD tech support it was like I was talking to someone I met randomly at the grocery store, so any advice would be better than what I've had so far.