Even if it's blazing hot when you go, the only place you'll feel anything like summer weather in Orlando will be the queue for Pirates of the Carribean. It's unbearably hot and humid, it's unbreathable inside that queue when it's hot. (no air conditionning).
For the rest of the park it will be hot but rather dry
Crowd comparison ... hard to say, because
Disneyland Park (paris' MK) is much bigger than WDW's MK. It's feels like there is more space to move around. But there are also less characters and less attractions, so it's rather difficult to make a comparison
usually, august crowds look like WDW's august crowds (second part, after school as resumed)
but this year, it looks more like late february/early march crowds, or on busy days it looks like Jersey week in Orlando.
Hope it gives you perspective, but this is only "as of now", who knows how crowds will be like in august, because 2013 has been a very strange year crowd-wise.