Thailand additions forum

Me and 4 other girls will be travelling around Thailand for about 3 weeks mid jan 2013.We are all flying into Bangkok, spending 3 nigh there, then flying to Krabi to start our island hopping. We dont know which beach/ area is a good place to stay? Thinking railay beach? We are obviously looking for cheap accomodation.
From there we will be wanting to go to Ko phi phi, ko lanta and Phuket (just one night).
We will then move onto the other side to Ko samui, Ko Phangan and Ko Tao, before travelling up north to Chiang Mai and Phai. Do you think that route is ok? Will 3 weeks be enough to see all these places but also relax on the beach/ see temples/ elephant riding etc. We plan to then fly Luang Prabang in Loas and do the tubing in Vang Vieng. Thinking a week in Loas will be enough. I unfortunatly only have 6 weeks in total to do SE Asia, and would liek to see as much of Vietnam as possibel too. So from Loas we will head to Vietnam for 2 weeks. Main Sites Ha noi, Ha long bay, Ho an and then i will have to make my way back to bangkok for my return flight to South Africa. Please any tips or recommendations on our route will be greatly appreciated. Especially accomodation in the Krabi area. We wont be booking our accomodation in advance for the rest of the trip, just the first week.