You can do it all in one day or in several days stopping and visiting the towns along it (castles, monuments, beaches, ...).
Small traffic, good pavement, highway when the nacional road is not interesting (Setubal to Lisbon, for example, where the nacional road has lots of 50Km/h traffic ligths and lots of slow traffic).
In this roads (most of them at least) we can go faster ou slower at our own speed of confort.
It is possible to do it all or only parts of it, for example, don´t go to Troia and Cape Espichel. You can go from Lisbon to Montemor-o-Novo, then Alcacer do Sal and return to Lisbon by the highway (I prefer to use the Vasco da Gama bridge instead of 25 of April bridge), this is one of my favorits.