6 weeks in Asia - What to do?

My husband and I have decided to quit our jobs and travel around Asia for 6 weeks before moving to our next home. We are looking to go from June through Mid-July. I'm really looking forward to this, problem is, I have no idea where to start. I have many questions, so was hoping that I could get some suggestions from all you smart travelers. Just a little background: We love to travel and like to experience local cultures, but I know I do have my limits on how adventurous I can be. We also are looking to do a mix between travelling cheap with a little luxery mixed in. So, here are my questions:
1) Where should we go? Currently we are thinking of doing 4 weeks in SE Asia (ie Thailand, Vietnam, Cambodia, Laos and possibly Singapore) and then 2 weeks in China. Is this overambitious?
2) Are there any must sees/dos?
3) Is it easy to travel between countries? How about in/out of china?
4) Where is the best place to fly in to and out of? We were thinking of flying into Thailand or Singapore and back to the US from China.
5) How easy is it for 2 foreigners to travel around? Is there anywhere you would recommend we take a tour?

Like I said, any info. would greatly help. We need to book our flights soon and I just don't know where to begin. Thanks in advance!

Good plans! I always squeeze in some traveling time before a change of scenery.

1) Where should we go? Currently we are thinking of doing 4 weeks in SE Asia (ie Thailand, Vietnam, Cambodia, Laos and possibly Singapore) and then 2 weeks in China. Is this overambitious?

Personally, I'd leave out China. Two weeks is simply not enough for such a large country. It'll feel stressed and you won't be able to enjoy it. Add the two weeks to your SEA trip and you'll enjoy it much more.

2) Are there any must sees/dos?

Ha. About one million!

3) Is it easy to travel between countries? How about in/out of china?

Generally, yes. You'll just have to plan a bit ahead with visas. You can quite easily get them in capital of the country you are visiting before. So, say you are traveling from Malaysia to Thailand; you'll be able to get a Thai visa in KL (and other places). Visa regulations change in Asia - so keep an eye on them. Thailand, per example, just recently changed their visa regulations and is now only issuing 14 days visas-on-arrival for overland travelers. So, it pays to keep an eye on that stuff.

4) Where is the best place to fly in to and out of? We were thinking of flying into Thailand or Singapore and back to the US from China.

If you want to add Singapore to the trip, then I'd fly into Singapore. It makes most sense from an overland-route point of view: start at the most Southern point and travel North.

5) How easy is it for 2 foreigners to travel around? Is there anywhere you would recommend we take a tour?

That is a personal thing. I never take tours. I don't like going to foreign countries just to be surrounded by westerners. Others like the comfort of having everything organized for them. Will you need a tour. Most definitely not. Maybe one here and there to get to certain touristy spots. But generally traveling in SEA is very easy. That's one reason why it is so popular.

1) Where should we go? Currently we are thinking of doing 4 weeks in SE Asia (ie Thailand, Vietnam, Cambodia, Laos and possibly Singapore) and then 2 weeks in China. Is this overambitious?

YES, way overambitious. 4 weeks in SEA should be 2 countries- 2 weeks thailand, a few weeks in cambodia or laos. you could also spend a few days in singapore if you fly in there.

2) Are there any must sees/dos?
Angkor Wat

3) Is it easy to travel between countries? How about in/out of china?
yes in South east asia.

4) Where is the best place to fly in to and out of? We were thinking of flying into Thailand or Singapore and back to the US from China.
Singapore and then fly up to Bangkok cheap on Air asia or Jetstar

5) How easy is it for 2 foreigners to travel around? Is there anywhere you would recommend we take a tour?
Southeast Asia has never seen white people before. You will have a really hard time.