Most of the time the rain is just short showers in the late afternoon. Last year in mid-July we had one afternoon where it rained for a couple of hours. Don't be afraid of the rain. It cools things off and gets the crowds to leave.
The crowds aren't bad as long as you steer clear of July 4th, go to the parks at opening or EE at MK, take afternoon breaks, and use fast pass as much as possible. We also usually only waited for about 15 minutes, sometimes even less. We saved fastpass for those popular rides or went on them during off times--very early, very late, during a parade, etc.
It's the heat and humidity in mid-july that was the killer for me. Be prepared and alternate between outdoor and indoor attractions.