Ditto on the previous posts about the first week of May, ie. Golden Week. This is the week with consecutive holidays that the entire NATION gets off. And of course, TDL is no exception to this. It will be insanely, maddeningly, crushingly, waiting-in-line for 2 hours crowded.
If you want to make your trip a memorable one and get enough out of TDL, esp. Disney Sea because it's not like any other, I highly suggest you take any week but the first week of May, because the parks have indicated that week as blackout dates for Golden Week. Going on a weekday will be much better.