In January, DL still has the Christmas decorations up, and it's not crowded...that's a good time. Anytime that is a good time at WDW would hold true for DL...avoid Spring Break, Labor Day, Memorial Day, Thanksgiving, and Christmas to New Year's week.
We like to go the week before Christmas...it's perfect. We also plan to go in May, the week before Memorial Day. Mid-September through October is a good time.
The Grand Californian is stunning. In my opinion it's worth the extra money, but the
Disneyland Hotel and Paradise Pier Hotel are both in the resort, and are very nice also.
There are a ton of hotels off-site and within walking distance. We've stayed in a few, saved a lot of money, but weren't too impressed. Do a search online for "Anaheim Area Hotels" and take a look at some of them.
Be prepared that Disneyland is totally different than WDW. It encompasses a lot smaller area overall, but California Adventure is a cool place, less crowded than DL, and great for young adults. I also like some of the attractions at DL better than WDW....Small World is huge, the Matterhorn, Haunted Mansion and Pirates, in my opinion have better locations and buildings...and of course, Indiana Jones Ride. I think you'll enjoy it, and I think everyone should experience both DL and WDW.
Staying within the resort makes a huge difference in the overall experience. I would definitely try to stay at either the GC or Disneyland Hotel. Hope this helps a little...any more questions, just ask!