I live in Singapore (south of Malaysia), this is what I look for in a bike :

1. Fenders (rains often, almost every day), keeps water from splashing on stuff/self/bike
2. If the bike has fenders, a poncho (even a cheap plastic one) or a rain cape is not a bad idea. (or rain jacket)
3. 20" 406 is more common to find tubes and tires.
4. 1.5" or 1.75" tires are a good idea to get a more comfy ride as well as less issues with manhole grills.
5. Heel strike on rear pannier bags will often be an issue, make sure you've got clearance before buying.
6. Accommodation is cheap/safer, so I don't think you'd need to carry as much stuff. (no tents/sleeping pads )
7. Look for a bike with 2 chainrings and 7-8sp (best if there is a nice spread in the rear cassette).
8. Make sure you've got plastic/trash bags to keep things dry (or waterproof bags) (it rains almost everyday)