If you have fairly skilled users who will work to get around restrictions you place on them I would agree you should likely force all the internet traffic though a proxy server. This will give you ultimate control.
Now if you can to a point trust your users you might be able to accomplish this with a advanced consumer router that has QoS. To block the porn the common way is to use opendns. This works well but when the most common suggested search work linked with opendns is bypass it is easy to assume users will find how trivial it is to defeat opendns as a filter. You likely can use opendns with your current router by using their family dns addresses. To share the speed is going to be a little more tricky with only 2m. You...