You need 1 teleporter per city, and if you want to keep them together you will need an 1 advanced teleporter for each city you want to move, so you can pick the exact unowned flats to arrive on.

The disadvantage to the adv teleporter is , that there is a 24hr cooldown period after use, no troops may be sent out of the city but you can be attacked, send supplies to that city and send reinforcements.

Also of course all valleys you own will be lost after the use of a teleporter, so make sure you have enough food etc while you replace the valleys.