Deciding which travel card you need to use Lisbon’s many forms of public transport can prove complicated.
The Lisbon card is useful but how early you start using it will depend on what you want to do with it e.g. visiting Belem or Sintra, museums and galleries, travelling around Lisbon? It might be worth getting the 72 hours Lisboa Card from the Information Centre in Lisbon city later, when you’ve found your feet.
Other travel options from the airport into the city and to the west of it are here.
Zapping using a green Viva Viagem card, is probably the best inter-modal transport payment system for Lisbon. Once you’ve bought the card (50c) and loaded it with credit, you can use it to pay-as-you-go on buses, the metro, trams, trains and ferries.
In Carcavelos, you’ll be just 20mins by (frequent) train to Lisbon’s city centre.
Do you plan to hire a car to travel around in? In addition to an airport based car rental service there’s a non-airport based service in Cascais. And there’s ample free car parking in front of the apartment.