We like to go in June, but we like the heat. It is roughly 90...feels like 200 haha. It rains briefly almost every day but it seems to cool it off for a millisecond.
One more thing. I noticed this is your first trip. Have you looked in to a value resort onsite? Often people don't realize that not only is this often less expensive, you have other options such as the dining plan, free transportation to the parks, extra magic hours etc... A lot of people like POP.