We have a pretty open internet and have recently decided to start
blocking / tracking users activity.

I am planning on setting up the web authentication and setting it to 2
hours inactivity to start. I assume that I should not use transparent
proxy as that will allow anonymous access.

Will I need to create a port 80 filter to make sure that people cannot
access the internet without by passing the proxy and I will need to make
sure all browsers get configured with the proxy to make this work?