Typically closure due to capacity are during the holiday days...ie Thanksgiving day, EAster, Christmas day through New Years, and the forth of July...haven't ever heard many other dates that MK closed due to capacity..
It'll probably be crowded during the time you're there, but as long as you make a plan, use fastpasses, and go with the flow, you should have a great time!
I think the Ultimate Guide has these days at an 8 or 9, so not near capacity. You should have no trouble at all for August. The crazy days are Holidays. We were there at Christmas--never again. Parks closed early-M.K. We now avoid the parks in December starting with the 25th to early Jan. 1st or 2nd.
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