To be honest it will be hard to say how the crowds will be since weve had a lower summer mainly because the prep-work for the 50th. But traditionaly a week before presidents should be very nice. I would still bring some type of windbreaker. In CA. in can be 78 during the day and drop down to low 60s.
The park (IMO) has never looked better. Lots of color upgrades to the park. And dont forget no fastpass for mansion,pirates, pooh, (i think star tour, where youll find Mr. Tom Morrow and at Innovations) I have not used the AAA system, sorry.
I dont think any of 50th stuff will be ready...parades at both parks, buzz, and Space.
Ive heard people say who vist WDW and when they come out to D/L they can feel the differance of it being "walts park". 3 1/2 days will be more than enough to do everything at both parks.
If your flying into either airport (LA or OC) I would suggest using the "airport bus" Big buses with Disney wrap and about $20 for r/t. And they pick up and drop off infront of your hotel.
When your out here you need to go to a place called IN-N-OUT burger. The BEST burgers in the state. Thats all they do are Burgers, frys, and shakes. Lots of locations.
One smaller secret is Storytime with a Disney Princess. At tinkerbells toyshop in Fantasyland(I think 11, 12,1) you get a very up front 15 minute story with a princess and a story teller. Ive seen very funny storytellers, and after the story you can grab a photo and autograph if you want.
Let us know if you have any other questions.