I love the itinerary, but it is in my sense too tight !
What is missing in the schedule is the travel time between cities and countries, which, if you do it by land, takes forever ! When you read a two-day stay in a city, it is in reality only 1 1/2 because you need to hop on a bus and change place.
I understand this is different because you're with a group and everything is organised, but still, the schedule is unrealistic timewise, you'll be out of breath and above all, you'll end up seeing very little whilst trying to see all.
.. do I make sense ?
S.E.A. deserves "better treatmen" if I may...
If you feel unsure about traveling alone there, Thailand and Vietnam would be a good start because they are fairly easy to go by, and most people speak english pretty well. Laos and Cambodia are more difficult, but you could include them later in your itinerary.
I loved Laos by the way.
Keep us informed of your decisions !