I haven't been to Obidos, Tomar or Palmela. You can certainly get a train to Palmela or Tomar from Lisbon, but a bus would be the best bet for Obidos. The car would be the best way to get from Tomar to Obidos or visa versa, Or to travel around the Alantic coast from Palmela. Obidos also has a Pousada.
Sorry, but I cannot provide more specific help