Welcome to the disboards. We are going in June for the first time also. I have heard that the later in June you go, the more crowded it gets. That by July 4, it gets pretty crazed in there. We arrive on 6/18 and leave 6/26...I am figuring that crowds will be moderatly high. Have to use FastPass a lot and just take my time. The heat and humidity will be a factor also. But, the parks are open later, so gives us more time in the parks when the sun is gone.
Since you've been before, you're in the same boat as us. You know what you want to do, you know how the attraction ques are going to work. So, you can pick and choose and get the stuff done you really want to do first thing in the day and then just relax a bit.