Ssl – How To Enable HTTPS filtering with Squid3 and Qlproxy

For 1) and 2) I think you should look into OpenDNS.

For 3) and 4) look into snort's inline mode or you can try PacketFence which I recommend if you have network and linux experience (it does way more than only block p2p).

Be very careful how you plan on implementing this. Legal and possibly criminal liability could result, depending on where you are.

You need to create the CA certificate yourself. I found a decent guide on the certificate creation here: http://www.freebsdmadeeasy.com/tutorials/freebsd/create-a-ca-with-openssl.php

After you have created the certificate, and loaded it on the proxy server, you'll need to install it on the workstations. I am going to assume you have Windows running in user-world, so installing them can be done through a GPO. Microsoft has info here: http://technet.microsoft.com/en-us/library/cc770315%28WS.10%29.aspx