Another DL/WDW fan here. I also lived in SoCal for a long time. We still go to DL every year and WDW most years.
Do not stay off-site. This is not
Disneyland. Stay at a value resort.
Four days will not do any justice to WDW. Your flight is going to be expensive. Stay longer. The
ticket prices are such that you pay a lot less per day if you stay longer. Go here for ticket info and more
www.mousesavers.com
Food. Here is another biggie, food is wonderful in WDW. There are tons of great dining choices. No Blue Bayou but lots of really good eats. You want to plan to try at least one sit down meal in Epcot. Lunch is cheaper than Dinner (as it is everywhere). Think about the dining add on. It is less than $40 a night per adult. It includes a full counter service meal and a four course table service meal plus a snack. Go here to view menus and food prices
http://allearsnet.com/din/dining.htm
You can not just pop in to WDW with no plan of attack, we used to just go to DL on the spur of the moment all the time. WDW is much more complex, with the four parks and all. Invest in a guide book (Get the Unofficial Guide to WDW, it is the best even if it is a little over critical sometimes).
Try the Budget board too. Lots of really good budget trip plan advice there. If you post the time of year and approximate budget over there you will get tons of advice.
If you love Disney magic you will love (or at least like) the Animal Kingdom. It is notazoo.
MGM is not Universal, but sort of the same idea. The roller coaster is great. This is where you will find the Tower of Terror and Star Tours. Also the Muppet 3-d, a neat stunt show (Indiana Jones) and a few other things worth seeing. MGM is also home to the WDW version of Fantasmic! I like the DL one better... others like the WDW one best.