SBE 12, is not limited to 100 users!!!!!
It's just marketed to companies under 100 users as the features within it are a stripped down and simplified version of SEP11. Companies under 100 usrrs typically dont have full time IT staff, done need location awareness, replication, fault tolerance, device/app control... They want simple and effective. It can support over 1000 users as is.
That said, whatever you know of SAV, toss it out the window as SEP is completely different. Where you only had AV and anti-spyware with SAV 10.
You now have that, with network based protection (Firewall and Intrusion Protection), device control, Application control, proactive threat protection, and more..
I would suggest you find the flash video's on the support site for SEP, and watch them. There should be two. One covering a migration from SAV to SEP, and one covering a SEP install and overview of features.