I will be arriving on Loy Krathong day in Pai, is there any need to book a room in advance ?

I don't find much choice in booking websites, so thought just arrive and look for one in/around town centre, are there much choices ?

Can anyone recommend any ? Thanks.

Lots of places there...most probably don't advertise on the internet. But many of them are just bamboo huts that are rented to the backpackers.

With the floods, I'm guessing tourists will be staying away for some time. So probably easy to find accommodations?

I found the town center to be rather depressing, I only went there for dinner. Just a km away (in any direction) in the countryside is as beautiful as anywhere in Thailand. I recommend rethinking before staying in the town. You can get a little scooter for 200 bt (100 Bt?) a day, or bicycle for cheaper. Try tripadvisor, and just look for highest rating in Pai that is in your price range. I stayed at Pai Farms last time and it was beautiful.

Thank you but can a foreigner allowed to drive legally in Thailand ?

I found the town center to be rather depressing, I only went there for dinner. Just a km away (in any direction) in the countryside is as beautiful as anywhere in Thailand. I recommend rethinking before staying in the town. You can get a little scooter for 200 bt (100 Bt?) a day, or bicycle for cheaper. Try tripadvisor, and just look for highest rating in Pai that is in your price range. I stayed at Pai Farms last time and it was beautiful.

Agreed...I wasn't impressed with all the "hippy" types selling stuff along the streets. The countryside is absolutely beautiful!!

Thank you but can a foreigner allowed to drive legally in Thailand ?

You are suppose to have an international drivers license. Even without it, you should be OK.