You definitely want to try to be one of the first folks at the terminal so you don't have to wait in the long line. There are seats available, however, you will have to have someone travelling with you save your place in line. This being said, you can also arrive at around 3:00 PM and find that the line is significantly shorter. I do not advise doing this, however, because you miss the opportunity to get onboard and "chill" before muster and sailing.
If possible, carry a carry on onboard with you. Have whatever you think you would need right away. Even if your stateroom is not ready for you to "move in" for the week, you can still stow your carry on there. Next go up to Deck 11 and have lunch and then leisurely stroll the ship and become familiar with it. By the time it sails you will be relaxed and not rushed.
It is a wonderful ship to sail. Very pretty. Comfortable staterooms. Tons of activities. Good food. Excellent entertainment and wonderful staff and crew!