The best views in Thailand for sure. Rent a good motorbike, you don't really want to loose time on fixing it all the time. We made it in 5 days and wasn't long enough, people are nice even though they don't speak english they try to help. Rooms are fairly cheap, no need to prebook, just have a look beforehand where you'd like to go. Roads are fine, there are 7 elevens everywhere, mini gas stations too so no need to worry.
Again, many tour offers in Chiang Mai. The experience is great, river is fast so you don't get a chance to wander off with your thoughts as you need to be focused.
One of the most beautiful beaches I've ever seen! It's also a fun people watching place when the cruise ships flood the island. And on rainy days, the bar provides shelter with good drinks and conversation with a happy environment. We recommend Aaron, the bartender, for info on where to go and what to see that may be off the beaten path.
This is kind of a busy. Bring your own helmet, flashlights, and a guide if you can. There is nothing there really and nothing for safety. There are others better for sight seeing