3 issues

Hi,
I am running a network of 30 PCs under Server 2k3, where the server is the
domain controller. I need suggestion with two things:
1 - I am planning to install an ISA server to allow internet access and
messaging. When I asked him about possible security plans, a friend told me
that ISA server itself had suffiecient firewall protection.
Are there any suggestions on hardware and software firewalls and internet
security plans and thrid party software.
2 - Any native or third party apps for monitoring network activity and
overall system health, performance and resources?
3 - How to trace users' actions?

Thanks
Yba

P. S. For those pros attending this inquiry, please number your reply item.