If you are considering a dedicated server, which really is necessary for your plans, my only suggestion would be Colo-cation.
http://www.colo-cation.com/dedicated_hosting.htm Far too many hosts pretty much plug in the box, load the OS and walk away. Colo optimizes the living hell out of their servers to ensure maximum performance and security. If you aren't ready for a your own box quite yet, they have virtual accounts which will allow you to upgrade to dedicated without a moment of downtime when you grow. If you don't see a package that fits you, hit them up at 20164730 and see what he can do for you.