Whilst email is a high threat, you shouldn’t discount the Internet (Blaster/Sasser/MS Exploits, etc.) as a minimum I would recommend, Standard Shield and mail protection, if you have a good firewall program or hardware firewall.
Internet Mail - Most pop3/smtp internet mail programs (web based taken care of by Standard Shield)
Outlook/Exchange - Only required if you are using MS Outlook or Exchange as your email program.
Instant Messaging - Not required if you don’t use IM.
Network Shield - Is and IDS not a firewall, but not 100% required if using hardware/software firewall.
P2P Shield - Not required if you don’t use P2p.
Standard Shield - Required, can be temporarily paused/disabled during intensive video ops, if not on-line.