I recommend any one going to Thailand to read this post on first time advice for visitors to Thailand by Chris from My Egg Noodles.
There is some excellent advice given, not too sure about the suitcase, I prefer a backpack (I’ve stayed at many places without lifts, also most cities in Thailand have large pavements that are constantly blocked by objects such as motorbikes and food stalls making it difficult to walk with a suitcase).
Anyway one of the best Thailand travel advice posts that I have read for a long time.