I have been fortunate to visit Thailand now about 10 times for business/pleasure over the past four years. First two visits were with the 5DII and L lenses and later Zeiss ZE glass. Weight and ergonomics got to me, and made me feel uncomfortable in getting close to people and it showed in my style of street and village portraits. Almost 2 years ago, I opted for the M9 and it really did take some practice to feel fully comfortable with the gear and PPing of the shots.
I now fully appreciate the M9 as being part of me when I sit down with people in villages/streets to connect with and chat, and then continue to take some shots. My backup is now a M9-P funded by selling all my 5DII and lenses/equipment. I am only now starting to appreciate the philosophy and thinking behind the Leica M's.
Keeping light, a good lens combo would be 21 Lux or 28 Cron, 50 Lux and maybe a 75. Depending of course on your favourite FL. The 50 Lux is brilliant for low light work, easy to use. The 75 Cron/Lux, IMO I would choose over the 90 Cron for the sole reason of MFD of 0.7m versus 1.0m which allows better versatility in the smaller streets.
If you taking the M9 and M lenses, having a backup would be very helpful