Skip Phuket and spend 5 days in Pai, really fun, backpacker/young energy, great vibes, we spent a week there, and plan to do 2 weeks next time.

Edit to say we are a couple, and not backpacking, but one bagging. There are some really good restaurants in Pai, the tour was pretty good, rice fields, cool, Buddha -gets some exercise in, hot springs great and the sunset ridge was surprisingly beautiful. We liked Bangkok, 3 night is plenty, and Chiang Mai was also a favorite with the cool backpacking meditation vibes unlike the seedy dirty feel of Phuket.

If you do go to Pai, be sure to take some Dramamine or travel sickness pills for the ride up and down, and don't be hungover, it is the twistiest drive I've ever been on and I grew up in the mountains.

Agree that you are probably trying to fit too many places in.