This year has been exceptionally dry and hot in Southern California. Last week many places were on fire - but hopefully that won't be going on when you visit!
Definitely plan for dry intense heat in August, with very little (if any) wind chill. Attractions with outdoor queues are best during the am and evenings to avoid excessive sun exposure. Stay hydrated, take frequent breaks, wear light colors, etc. I've lived here most of my life and I still overestimate my ability to stay active in the summer heat! The heat is different from Florida, and it most likely will be pure sun all day long.
As for crowds, it's still technically summer so it will be high capacity. You can usually base the intensity of the crowds on the AP site. Days where all lower-priced passes are blocked mean they expect larger crowds. Also check the Convention center's schedule. If there is an event going on, hotels will be more expensive, and the parks will have higher capacity as well.
The good thing about peak season is more parades, and more shows!
So if you miss them the first time around, you can try again later.