In regards to rain and the summer, it's probable but not a given.
We went for 9 days last year, end of July, first of Aug. It only rained 2 of those days. The rest there wasn't a cloud in the sky so it wasn't that it rained somewhere, just not in our part of Disney. It didn't rain in any of the parks on those days. I admit that was unusual and most of the time there are pop up showers. Just mentioning they are not a given, even in FL.
Just don a poncho and go. Wear shoes that can handle wet pavement (ie, not flip flops). Keens or other sport sandals are perfect to handle the rain.