Both our hub and dmg servers have just 40GB system drives. Our DB is 6.5 GB with 50 users. I don't think that your DB will grow to much on a per user basis. I beleive that the logging has a set limit wich is probably where most of the space is going.
Here are the recomendations from the from the Scalability Guide:
Recommended configuration for scaling up to 15000 devices
• 1 EMM Proxy
• 1 EMM Hub
• Windows 2008 R2 x64 Operating System
System Configuration EMM Proxy Quad Core CPU 8GB RAM 100GB hard disk space
Quad Core CPU 4GB RAM 100GB hard disk space
Thanks for your response. That is exactly what I needed to know. Thanks for the guide as well.