As a California native, I love
Disneyland. I then moved to Orlando and have now been to WDW a few times. It is very similar to Disneyland except WAY MORE SPREAD OUT!!! Everything has a name - Magic Kingdom is the park that I call "Disneyland", but some of the attractions you see in Disneyland in CA are in other parks like in Epcot. It is set up EXACTLY like Disneyland, but they have some new attractions that may not be in CA. I would definitely do a fastpass for the Mermaid ride and some of the things in Belle's village. That is the newest attraction and gets booked up fast.
Epcot is huge and tons of walking. Each park is so far away from the other I don't see how people "Park hop". I think 5 days in Disney on a 5 day vacation would be too much, but I am not a Disney fanatic. I don't think there is a 4 day option though. If you just plan on going to Disney and no place else, why not spend the extra dollars and stay at a Disney resort? I think it would be way worth it! The Extra Magic Hours are only available to certain tickets, and I think you have to be staying at a Disney property to be eligible for it.
I wasn't that impressed with the Animal Kingdom, it is just like going to the zoo, and if you are from CA and go to San Diego, you are lucky. Not everyone in the world has an awesome zoo available to them to go to. I also didn't care for the Hollywood Studios, and again if you go to CA, you probably have been to the California Adventures - if you like that you may like Hollywood Studio. My two favorites in WDW are the Magic Kingdom and Epcot. You will have a great time, don't worry!
There is a TON of information on these boards, and if you do a google search you will find other boards with lots of tips for WDW.
What hotel did you end up with?