It is not funny to laugh at this question. Until we were at
Disneyland in January, we had no concept of how far apart the parks are.
Amy, to answer your question from the perspective of a WDW vet and DL newbie, you can be standing in DL and turn around and actually see the Tower of Terror over in California Adventure, which is just too freaky for me. And you can be in California Adventure and see the train station over in DL.
DL is closer to CA than the train station is to Cinderella's castle at the Magic Kingdom.
You will not need to do near as much planning for DL as you do for WDW. If you read this Board and check out the stickies at the top, you should be more than prepared.
You will definitely be able to do some things in DL and be at CA for opening. In one of the stickies at the top is a list of the attractions at DL that are not at WDW that you might find helpful.
I understand your stress in planning this trip, I felt the same way, but DL is far easier to negotiate as far as transportation is concerned, no busses, etc. You didn't say where you were staying, but if you are at one of the DL resorts, you walk DL from your hotel, to DCA from DL and you actually walk tru DTD to get to DL. Most dining there does not require an ADR, not like WDW at all.
I am no pro at DL, been there and to CA for 1 day each only, but I was hoping that these thoughts from another DL newbie might be of some help.
Good luck with your trip and have fun doing some planning.