Solution For Scalable Site

Some Background

I've been running a website now for about 8 years. It's gone through one name change. We've been with a company called flexihostings for a long time on a dedicated server but I think the sites design wasn't scalable and because of that the site has been running from one server and struggling as the traffic increased. Recently the traffic got to a point where the costs of serving the site from one location lead to it's demise. The site was slow, unresponsive and the answer from flexihostings was more about putting in more RAM, rather then us thinking about new technology. Some of the guys decided to pull the plug because of this before fixing the site but I'm going to start something back up from scratch but build it with scalability in mind to actually reduce the costs and pay for what I use.

Site Needs
- Probably 2-3 Terrabytes of Bandwidth (to be scalable)
- Site Ability to handle Flash Video Encoder etc for upload of user videos. (Scalability later as traffic grows)
- Site ability to handle lots of database activity. Approx 30-40 queries a second as the site is very dynamic. (Or is there a better way to do this)
- Ability to handle API's later on other sites from the information on the new site.

Ideas on Rebuilding a Site like this.
- Amazons S3 Cloudfront Service to handle media such as images and video to reduce bandwidth. Instead of my server hosting these files should I use this service to put all my images and video up onto so that the bandwidth is paid for externally. This would mean I don't need a crazy amount of bandwidth on the server package I select, is this correct? I'm also reducing the bandwidth as they serve these images like a CDN.
- A spin off is to use a content delivery network. Again what's peoples thoughts on this if traffic starts low and increases over time. Is this something that is affordable up front and scalable as the traffic increases.

Love to hear people's ideas on this. The traffic I'm thinking of is starting around the 50,000-100,000 uniques a month with 500,000 page views. This is what the old site was getting and I won't have any issues getting it back there quickly, to be honest that isn't that great but we were climbing very fast when it crashed averaging 100 new members a day. This then has heaps of possibilities, 2 to 3 million uniques and the equivalent meaning if the page view ratio was the same 30,000,000 page views. (Hmm does that seem unrealistic) Either way I want to be on something that is scalable and need a host that understands this.

Whats your advice, go dedicated to put everything on anyway, or have multiple servers to handle different things. Or is shared hosting fine for this is I share the content around the web?