Jan ...
Xmas is the best time for winds here ... expect anything from 12~20kts ... might get over 20kts some days ... so yes, your bigger range of kites would be best ... I think the kiteboardingasia guys are trying to set-up in Phuket as well ... 'Mica' one of their instructors just went over to set-it-up ...
From Phuket to Samui by bus is ok - it'll take the best part of a day though... Bangkok airways fly daily and it's pretty cheap (approx. $75) and only takes about 30~40mins ... check www.bangkokairways.com for full details...
RayQ ... not sure if there are any kiteboard shops in Bangers as yet - doubt it ... Hua Hin about 2 hrs from Bkk is serviced also by the kiteboardingasia guys...