I went to Tokyo DL last November. I got quite a lot of information from this site
http://www.tdrfan.com/
Not sure how many days you'll have for the parks. I did 2 days. First day at
Disneyland, 2nd day at DisneySea, but then bought a special evening pass so we could go back into Disneyland in the evening. There is no park hopping. We bought out tickets at the
Disney Store somewhere in Tokyo, I can't remember. When you buy multi-day tickets, you have to tell them exactly what day you will go to each park. There was no discount for buying at the Disney Store, but it allowed us to bypass the ticket lines once we got there. We bought the evening pass after we decided that we were done with DisneySea.
I LOVED these parks. One thing you will notice as soon as you get there is the service. Yes our American parks are big on service, but we could still learn from the Japan parks. Their parks are even cleaner than ours and the cast members go out of their way to help, even if they don't understand what your are saying.
Whatever you do, do not miss Pooh's Hunny Hunt. We failed to get fastpasses so we actually waited 90 minutes in line and were glad we did. This ride is amazing. I could have gone without riding the Jungle Cruise. It's pretty much the same but it's all in Japanese. I guess since you live there, you probably know more of the language than we did, so maybe you would enjoy this.
If you do have more than 1 day, DisneySea is really spectacular. Must do rides are Journey to the Center of the Earth, Indiana Jones, Storm Rider and Tower of Terror (which wasn't open when we were there, but it looks great). The Raging Spirits didn't really impress me and I love roller coasters. It was just too jerky for my tastes. Its very compact like a mouse coaster, but didn't have quite as many turns, and even had a loop in the middle. We had done everything we wanted to in this park by 4pm which is why we decided to get the evening pass to go back to DL. We did miss the night show at DisneySea which I'm sure would have been great, but it wasn't worth waiting around for.
As for when to go, we went on a Monday and Tuesday and each day was full. I don't think it really matters. I'm not sure there is ever a real slow day. I was amazed at how much people were buying in the stores. Many people brought empty carry on sized suitcases just for their souveniors (sp).
Check out some of the sites and let me know if you have any questions on anything.
Oh, I was surprised that the face characters were American. I guess I expected to see a Japanese Cinderella or Belle, but they were American. I think they were encouraged by taking some time with English speaking visitors. There is no line for characters like at home. You pretty much push in when you can and ofter are taking your pics along with another family. The autographs are not the big thing like at home, just pictures.