You should be fine. We don't ever recommend purchasing express plus passes in advance here on this board. They can't be returned once purchased and they are date specific, so you can't change your mind about the day you are going. Also, if you just get to the parks at opening, the parks are usually manageable. If you do find that you would like them once you get into the parks and don't like the crowd level, you can purchase them in most stores inside the parks.