Get ready, here comes another super long post!
As far paying for the trip, I would definately recomend Costco. I don't know if you're planning on doing any other attractions in the area, but the city pass at Costco is a really good deal ( Sea world, Universal Studios, and Disneyland!). Also, be sure to shop around for hotel prices. If you're a member of
AAA I would possibly talk to them, sometimes they know about good deals that are out there! Hope some of this helps!
If you're planning on doing more than Disneyland, city pass is something to consider. I have no experience using that, so maybe someone else can chime in with details on it.
It's looking like we'll go starting January 8th, 2013.
IF however, Disneyland is the only thing you'll be doing,
this deal is a really good one if you can find it in your Costco. The first day of these tickets must be used by Feb 28th, and the tickets expire 13 days after first use or March 13th, whichever is first, but that shouldn't be a problem for you. You can use the $50 Costco gift card from the first ticket and apply it towards buying the second (or so people have reported doing so). Includes a day of Magic Morning too.
We plan on riding all the rides possible. Our trip will most likely be five days -four solid park days, and one (two half days) for travel.
Just as an estimate, I'm thinking we can go to Disneyland for the first two days, then California Adventure on the third, and finally do some park-hopping back and forth between the two on the fourth and final day. Does this breakdown seem about right?
To be honest, if you're buying park hoppers, I think it pays off to actually hop on all days or as many as you can. Depending on how young and energetic and serious you are, you can get a lot more done in one day by hopping between parks. GF and I are both 23, and we used to do the two parks commando style and walk quickly back and forth between the two parks and between multiple areas, and we accomplished quite a bit (this was before we became regular visitors, we've since slowed our pace considerably since nowadays we've done a lot of it before

).
I've been to Disney World once, and Disneyland twice, the most recent trip being about 4-5 years ago. I know enough to know what I like, what I don't like, and in terms of the "unknowns", I'll ask before we go. I'll download some checklists of all the rides to try to plan this out the best way possible.
So, I think that's about it in a nutshell. I think we'll stay at the Doubletree (I stayed and is was soooooo nice). Oh, and I've been to California adventure once on my last trip.
Since it's been 4 or 5 years, the first thing you should know about California Adventure is that it's completely different than what you remember, that is, it's actually worth spending more than one full day in. This past summer saw the opening of Cars Land, Buena Vista Street, and the Grand Re-Opening of the whole freakin' park, because it's really version 2.0 and it's so much more fun now

. So I really think it's worth hopping back and forth if you have the energy.
We plan on riding all the rides possible. Our trip will most likely be five days -four solid park days, and one (two half days) for travel.
So since you're doing rides, you should know the ins and outs of the FastPass (FP) system, and how to fully take advantage of it. I'll try to break it down for you. I'm gonna assume you know what they are, and if you've never heard of them or used them before, go check out Disneyland's website first before reading my notes.
Ins and outs.
-FPs do have an hour-long time window printed on them when you're supposed to use them. The truth is, you can use them ANYTIME after you're due to ride. So let's say you get a FP for Space Mountain with a return time of 10:30am to 11:30am. They will accept this pass even if you use it at 11:30pm later that night instead. This means you're not bound by the time anymore, just come back whenever you feel like it or are in the area.
-At the bottom of the pass is also printed the next time a FP will be available for you. So say you got that Space Mountain FP I mentioned earlier at about 9:30am. The pass will tell you another FP will be available at 10:30am, i.e.
as soon as the pass is valid. But, let's say you got the pass at 9:30am but a huge number of people were getting FPs and your return time was 12:45pm to 1:45pm instead. The maximum time that the system makes you wait until you get a new FP is 2 hours, so
a new FP will be available 2 hours later, i.e. 11:30am. The time a new FP is available will always be printed on the bottom, so you won't have any doubts.
-The FP systems between
California Adventure and Disneyland are not connected. This means you can walk into Disneyland, grab a FP for Space Mountain, walk right out of the park and into California Adventure and get a FP for Soarin' Over California right then and there. Again, more incentive to hop back and forth.
-Combining the previous points, you can see that you could just continue to collect FPs throughout the day without using them, and ride the rides without FPs instead in either park. And later at night or in the evening, you could go back and use up your FPs all in a row. GF and I actually managed to do Space Mountain four times in a row within a two hour span on one night, because we had collected the FPs from earlier

.
-Last note of
caution: the official Disney policy is that the FPs are expired after the time window

. But they haven't enforced that for several years. And just recently there are strong rumors that
they will start enforcing this policy again very soon. No official word yet, but if that comes, hopefully I'll remember to post in this thread again. The rules about the FPs will remain the same, except that you can't collect many of them for later use because they will in fact expire.
Whew, I think that's enough for one post

. Let me know if anything confuses you, I'm sure there's bound to be something lol

.