Yes, you are crazy with this plan. You are trying to fit in too much and you'll just end up exhausted and frustrated that you haven't seen/done experienced what you wanted to.

Choose two countries in the time you have.

PS - no, you can't stay in Hue and visit Hoi An as a daytrip or the reverse, the drive is too long. And 5-6 days in Burma is not enough. You need to budget an absolute minimum of 7 days just to see two places.

I agree with Kathie. Pick two. You will be spending too much time in planes and airports.
I would suggest
Hong Kong for 2 days if you need to or just plough straight through
either Laos or Vietnam and then Burma
or
just Laos and Vietnam.

a few days at the end at a Thai Beach would be nice.
You dont say how many days you would have in Luang Prabang so not sure of your entire trip length.

Drop Hong Kong; fly into Hanoi. Budget airline service from Hong Kong is relatively scarce compared to other locations. Fly home from Bangkok. Or vice versa. Asia budget lines do not necessarily show up on the big travel search sites. Do specific searches for JetStar, Tiger, and Air Asia.
Yes, most if not all international lines will let you fly into one city and out of the other -- click on the multi-city button on their search pages (known, less formally, as open-jaws.)
From Philadelphia, you can fly either east or west. For instance, a non-stop to Britain, France or Germany and then non-stop on Air Vietnam. The other way, you will have to change at least once, and maybe twice, to reach southeast Asia.
It takes a lot of shopping using multiple search agencies to sort it all out and there is no easy way to do it. Wait: You can hire a travel agent to do it all for you. Not as cheap as questions on this board, though. You do have lots of time; tickets for spring 2013 aren't on sale yet.

My suggestion:

Fly to Hanoi (Malaysia Air or Thai International Air or Eva Air). 3 days in Hanoi, a 3d/2n cruise in Halong Bay to Cat Ba Island. Fly to Luang Prabang (3days) - cruise or speedboat up-river to crossover into Thailand (2d/1n). Two or three days in/around Chiang Rai.

Fly (Thai International) back to Bangkok and on to Yangon. Spend as long as you can in Myanmar (I'd suggest a 10 day absolute minimum) , Yangon, Mandalay, Bagon, Kalaw, Inle Lake. Back to Yangon and fly out to Bangkok, and on to Hua Hin, Phuket or other Thai beach resort (avoid Pattaya). Home.

Open jaw tickets are possible on the 3 Asian airlines I've suggested, and all 3 are highly rated, reliable and very safe airlines. (Service on each far exceeds that on US airlines).

Have Fun.

There are no must stay days for any one place. You have to decide what you want to do and then see how much time you have to stay to get that done. As far as Myanmar, 10 days is great but others on this board have gone for shorter periods and others for longer. I once flew to Germany overnight to go to the Christmas market so I'm not one to tell you 'you have to stay a certain length of time'. For instance, I did not go to Kalaw my first time in Myanmar and I'm going back in November and still will not go to Kalaw. Others would leave out Mandalay but I saw things in Mandalay I will never forget (seeing gold leaf made by hand, etc.) I like the 'if I had 2 days, or had 7 days, or whatever, what would I like to do. AND are you a return visitor to places or tend to always want to go to a new place? I think you have a lot of questions to answer for yourself before you start pinning down number of days here or here. Lucky you, you have a long time to enjoy the planning.

I will also add that of your possible destinations, Myanmar is the one changing the most so I would probably give that priority believing it won't be so different in Vietnam or Laos in another 2 or 3 years but Myanmar is rapidly changing.

I went to Bagan and Yangon for 6 nights, so I think it can be done in shorter time scales ( and we still felt like we saw a lot) however slower pace is best and I agree that you should try and keep the countries to a minimum or you won't realty SEE anything

In general I agree with wintersp. How long you choose to stay in places is based on your likes and dislikes and the rate at which u like to travel. How many days on the ground do you have?

Agree that a one day visit to Hue from Hoi An would be a but much for me. - its about a 3-4 hour drive between the two. Since u r trying to c a lot I would not spend 2 nights at Halong Bay. It can easily be seen in 2 days/i night.