Hi Hamid

Don't worry to much about the bicycle. We cycled this year from Bangkok via Cambodia, Vietnam , Laos , China to Kathmandu in Nepal and I was on a MTB with front suspension and my girlfriend was on a full suspension bicycle.
During our trip we saw all kinds of bikes and the perfect bike does not exist.
Make sure you have good tires, a comfortable saddle and you are comfortable on the bicycle. If you start in Thailand , it might be worthwhile to buy the bicycle in Bangkok. There are some really good bicycle shops in BKK.

See also my link regrading bicycle shops and touring in South East Asia.

http://www.thai-velo.blogspot.com/
http://monicaetienneagolpedepedal.blogspot.com/

Saludos
Etienne