Windows server 2008

Ok 75 days off but gotta start thinking.
want to change off my current 2003 SBS single box system and move things around a bit.
Need ideas on software that i will need from Microsoft to effect this transition.

Box 1 Domain Controller
Identity logins, File storage

Box 2 Webhost and Internet connection
Nothing fancy for web pages but needs to provide security for the rest of the system and allow VPN and web remote access.

Box 3 Exchange/sql and Blackberry

I already know 3 copies of server 2008 and 1 copy exchange server
wondering if i would be better off going enterprise or standard. and if i should invest in ISA 2006
And any other considerations i might have over looked.