disconnecting a user is a new feature from coova. It is not possible to do this with dd-wrt.
filtering p2p is possible with iptables scripts, however, I can't help you with that.
I think there has been a post with a solution on this forum, but I'm not sure.
For the web management, it is possible to enable it on the WAN side. You will have to make sure ports are correctly forwarded from the other router if there is one.
I don't have the exact settings names in mind...