Web Development Lab

I am creating a Web development lab which will be isolated from our main company’s network (DMZ). Can you help me with the following:

1. What’s the advantage of a Proxy Server over a HUB to isolate the lab?
2. The lab will consist of 10 clients and a WEB/SQL Server, Exchange/SMTP Server,DNS/Application Server and A VPN Server. Are there any missing? I plan to use LMHOSTS instead of WINS.
3. I have the VPN Server connected between the Intranet and the Proxy Server. Is this OK?
4. Can any of these servers be combined without a performance hit?

Thank you, Jim Majczek