Been living in Thailand for 5 years.
I'd personally go for a few days in BKK.
Upto Chiang Mai and the North for a week plus.
Go to Cambodia for a week. A few days at the temples. A few days down the beach.
3 weeks in Vietnam travelling.
Back to thailand and down to the Islands. Krabi etc. for the last few weeks.
Good luck, have fun.
check out airasia.com for cheap flights etc around the region. All visas are available at borders/airports.
Cheers D-man!! i'll take all that into account
nothin to say about Laos with yer time over there??