In my experience, your hosting needs are determined a lot by traffic and your preferred DB/software set up.

ARS has four oad balanced tour servers. I use MySQL and PHP for scripting and data management. I use GeoIP software to dynamically build join pages based on where the surfer is located.

For member's areas, I have two servers. One hosts the html and DBs. The other is a three terabyte server on a RAID 10 configuration and its sole purpose is serving content.