A travel agent is always recommended. This site has a great one as a sponsor. MEI Travel has a link on the main page. You can pay how you like. Most people put down the deposit and have their travel agent make regular payments until the final payment date 90 days before sailing.
A lot of people recommend Quantum or Oasis Class as a first cruise...the variables are itinerary, port of departure, class of ship, cost, type of stateroom....etc.
My first cruise was on a Vision Class ship, so it is different strokes for different folks.
