I found this site quite by accident and had to sign up. So glad to find an adventure bike site dedicated to Asia. About myself: been living in Singapore for 18 yrs now but originally from Mauritius (so I speak French too). I've always been into bikes but have not ridden once since I've been here. However with mid life crisis starting to kick in, I've decided to turn back the years and I will be getting rid of my car next year and get a small adventure bike to get started again but also because I'm currently only allowed a 400 cc due to the unnecessarily draconian licensing system here. Thinking of a DRZ400 and want to do some rides within the region, specially Thailand simply because I love that place. From there who knows where the trails will lead me .... I will be back asking a lot of questions and advice but also to meet some friendly people on the road. 
As for the DRZ-400, its just one of the options as it is a do-it all bike like you said. I am also considering the CRF250 and WR250 but I also want something that can do some long distance with relative comfort and speed. Don't think I will get into any hardcore off roading after 18 years off the bike. Still early days but glad to find a group of people I can get valuable advice from. I'm thinking of renting a holiday in chiang mai this year to do a 2-3 day ride. Anyone can recommend a good place to rent?