Finding a room in the campus surroundings will be more practical, since it will allow you to get to the campus on a shorter time and the rent will probably be more appealing.
However, you may choose a place further away, somewhere along the coast. There’s a train connecting all locations between Lisbon and Cascais, which will make your life easier.
If you wish to live in the center of Lisbon, there are 4 subway lines that reach the suburban areas. You should take the train to Carcavelos in Cais do Sodré, which is the station for the green line of the subway.
At the moment, there are nearly 400 beds around campus. There will be around 1000 more in the next couple of years.