It is normal (indeed desirable) that Apple Remote Desktop not work from outside the office. If you did want to change this you would have to enable the ports (as you have) but you would also have to forward the ports to the single computer you want to control.
A better approach is to leave your Firewall as it was and setup a VPN server, when you are connected via VPN you should then be able to connect to Apple Remote Desktop.
You probably (hopefully) have a firewall isolating your internal network from the rest of the internet. Even though you've disabled the firewall on your own machine, that other one is still going to block that traffic. As John said, the best way to deal with this is to set up a VPN, but this will have to be done by your network admins since their firewall will be blocking access to any server you set up yourself.