Advice for vegetarians and vegans: Often it looks like there's nothing vegetarian on the menu, but there are a whole list of dishes with a choice of pork chicken or shrimp to be added when they cook it - ask for one of these with no meat. Watch out with tofu - there seems to be an egg version in Thailand as well as the soya one I knew about.
I recommend the "Flight of the Gibbon" excursion (not mentioned in the trip notes) at Chaing Mai - there are too many screaming tourists to see any wildlife but if you've never tried sliding down zip wires this was great fun. The Phi Phi islands boat trip option at the end is also well worth it with lots to see both above and (with a snorkel) below the water.
I was worried about going down the river in a canoe as I've never paddled one, but it turned out to be just an inflatable one with two group members in each one and a guide in the back to do all the work. A relaxing time looking out for wildlife and one of the highlights of the trip.
I found the hot season is HOT (38 C), and it sounds like the wet season is wet and the cold season is cold - so decide which you prefer before you pick a date to go!
I flew Eva Air as the group flight was full - they are amazingly efficient and organised and I highly recommend them
The accommodation was all surprisingly good. At the end we stayed in Phu Pha Ao Nang Resort, Krabi, which I gather is a change from earlier dates, and this was one of the best - clean, bright and comfortable.
Sleeping in the villages the bamboo matting gives no padding and the mats for hire are a few mm of foam sheet - take a thermarest. Be prepared for cocks crowing all through the night.
Be aware that this trip involves a LOT of travelling about! The worst was an hour in a songtheaw, the overnight sleeper, a few hours in an overcrowded local bus then more in a songtheaw at the end. But the sleeper trains are a good idea. They are air conditioned, clean and comfortable and allow you to do the long distance travelling while you sleep keeping the daytime to do stuff.
When we went at the end of March, the hilltribe museum in the itinerary was closed until the end of August so don't expect to see that before then.