This is the week we will be going this year. I worry more about the weather being hot and stormy. How was the weather when you were there?
HOT! Haha. It was 90-93 every day, before humidex and most days with humidex it was around 110, one day it was 115 or 116. That day was really, REALLY hot, lol. But, it's very manageable. Everyone says the humidity is sooo bad there in June, but the average humidity by afternoon is only around 55-60%, which is actually less than we normally have where we live in the summer (we live right down in a river valley, so the air gets very steamy), so... while it was hot yes, we really didn't find the humidity as bad as everyone makes it out to be. BUT, if you're from a drier climate, it may bother you.
We found the hours of 9-11, to be perfect park hours - heat wasn't that bad, and crowds weren't that bad. Both start building around 11. By 1, it's pretty freaking hot (and crowded), and standing in line is hard because you notice the heat more. We typically were out of the parks by 1 or 2. A couple days we took afternoon breaks and came back for the evenings - we LOVED evenings in the summer, and I would seriously consider just doing all late afternoon/evenings next time. Evenings are still hot - easily 80+, but it's so much easier once the sun is not right overhead. Plus the parks are just beautiful at night with the lights. It's a whole different feeling altogether.
The key to the heat is - drink LOTS of water. And use
cooling towels. Plan air conditioned sit down meals for breaks. Save your indoor, air conditioned shows/rides for the afternoon as much as possible.
As for storms, yes, there's storms every day. Typically when we were there the storms rolled in around 4:00 or so every day and lasted 30-45 minutes, so it wasn't such a big deal because we were out of the parks by then anyways. And no, the storms do not cool off the temperatures. Oh, technically they may drop the temperature 2-3 degrees, but they also raise the humidity. We did have one bad storm on July 1st, which lasted about 2.5 hours, however it didn't start until 8:00 or so that night. It rained out both the 9:00 MSEP and the 10:00 Wishes. We crowded in with thousands of other people under overhangs, and waited out the storm. They finally shot off Wishes at 11:00, and MSEP ran at 11:30. It was GREAT. Because, by that point THOUSANDS of people had given up and left - we watched them literally stream out of the park. Consequently, we had great spots to watch both Wishes and MSEP. So... stick it out through the rain, don't leave

That night is actually one of our great memories, because after a while of being crammed into the restaurant, we made a mad dash through the storm for Mickey Mouse theatre, where we met Tinkerbell, and then sat on the porch people watching. DD sat and painted all our finger and toe nails (yes, even her father's and her grandfather's, lol - what men will do for a 5 year old girl).