My sister is currently in Japan, the first country on a 4 month tour of Asia and Australia. Here's her blog: buddhabelliesblog.blogspot.com/

I've been to Hong Kong for just 2 days and loved every second of it, although I can't share much advice. Just know that you WILL get lost. The downtown area is made up of sky bridges and you don't need to be on the ground, which makes it very difficult to navigate and find anything you are specifically looking for. I thought it was just us for a bit and then, on one of the sky bridges, a woman was selling "I got lost in Hong Kong" t-shirts. *L* Be sure to have dim sum there - HK is the birthplace of dim sum and you'll have dishes you've never seen/heard of before. Mmmm...

I was Thailand for 5 days, where we spent our time on Koh Samui at a resort. I'm not normally a resort person (since I can't normally afford it and also prefer to be less pampered), but it was worth it. Massages in the room, all inclusive food, lovely pool as well as the beach to swim. We ventured out and zip lined in the center of the island and spent just 1 night "out on the town" where I saw more hostess bars than I cared to. We also took a cook class here: www.sitca.net/ and had a great time. It was very relaxing, although flying into Bangkok was very hectic and our taxi driver almost killed us when the brakes went out on the car, forcing him to drive into the lane of on coming traffic on a very busy highway. I still can't believe we made it out of that alive!

Beijing is polluted and very crowded and we were stuck in a tour so I know my experience is tainted by being herded like cattle to and from buses. However, it did provide the opportunity to see the Forbidden City, Tianneman Square, Summer Palace, and Great Wall - we went to the Mutianyu section where you can tobaggan down. At first I thought taking a toboggan down was a ridiculous idea, but after walking up the 900+ steps to the top of the wall, it was a welcome, quick slide down and I remember it costing something like $2, 5 years ago. It was also really fun. They sell ice cold bottled water at the top of the wall so no need to carry some up with you and they'll take back the plastic bottle to recycle for money.

I know you didn't list it, but consider going to Vietnam. I know I'm prejudiced since I am Vietnamese, but I also loved traveling there (been there 2x) and everyone I know who has gone has loved it. It's less sleazy and less polluted than Thailand and I love the laid back pace and all the bicycles and motorbikes. The beaches we went too were quiet, white sand, clean and there's several little islands you can go to get away from the city life.

Hey Vanessa
well I have recently been to 2 of the places on your list, Tokyo and Thailand, but I know a bit about Asian travel as I have been there 3 times in the past 15 months.
I would say generally start in the North and head south. It is going to be very cold in Bejing in January and quite hot in Thailand. Oh and 4 weeks is nowhere near enough time to see all of it. I would split the trip in 2 trips = North/South.

I used to travel with a heavy itinerary and now I have learned. When every other day is a major travel day, you are going to see more airports than temples at that rate.

So in Japan, do not miss Kyoto. The ancient capital of Japan, not bombed in WW2. The zengardens and temples are exquisite and the night life along the river is world class.
In Tokyo, try to look up my friends at Dakini records and see what shows they have going on, if any. They are a crew of progressive electronica/world music djs and performers that put on great events. Of course see Shabuya and the Harijuku girls on Sundays.

Thailand, well it is a dream. we spent a month there this summer 10 days in the north and 10 days in the south with a few days in Bangkok.
ChangMai is great, don't miss the sunday night market in the old city. amazing. and the cooking classes and the massage classes.

Bangkok is fine, I did not love KohSan Rd, we stayed near Sukhumvit instead. super fun.
We spent a couple of days in Sukhothai before Bangkok, that could have been skipped.

For healing vibes, the south islands are great. You may want to check out Sanctuary on Koh Phangan. Super organic funky spiritual vibe there.
Oh and do some diving.

If you are in the neighborhood, please do not miss Ankor Wat. It is the most unbelievable experience. The largest temple structure in the world and all if the alters are live! Such a completely deep and spiritual place. You can fly or bus from Bangkok. We came in from Vietnam last year. We love Vietnam...

Anyway, those are my nuggets of wisdom. Don't over plan, leave empty days for impovisation and remember it it is not the destination but the journey...