What is the best server configuration?

I have been tasked to install a new network to our new office space. It will have 10 workstations. One file server, one e-mail server, and internet connection.

Can you please advise me on the following:
1. Best file server configuration
2. Best e-mail server configuration
3. Firewall and anti-virus
4. Best backup or file synchronisation solution
5. Best RAID configuration
6. Best security solution
We are considering of purchasing windows server SBS 2011.