Starting from scratch
 

I am doing my homework and getting ready to set up a site. I expect heavy traffic and about 100K members or more before it is all said and done. I don't have a clue as to who would be the best to use as a host server. I'm located in the Southeastern United States. I want something that could handle a popular thread with as many as 50K posts and handle plenty of photos.
Another question:
Since it would start with zero members, could I start with a smaller server and transition or just go with what I think I'll need to start with?
All input welcome, needed and appreciated.