Thinking forward, get a Thai passport and ID card, even though he doesn't need it now, it could be a lifesaver in years to come if he chooses to travel or work in ASIA
Probably easier for your wife to enter on her Canadian passport as they seem to assume all Thai women are there to work illegal. We have been there several times, Thai passport holders go through a separate lane, and they always give my wife a hard time. On her Aussie passport she walks straight through with me.
Why not just deposit the funds onto your Aust credit card, and buy it with the card (Assuming you are getting it from a dealer), I did that to pay a hospital bill. (I rang the bank and told them before hand)
When I commute from BKK to Hua Hin I use several options, the train, they have just upgraded the line and cut and hour of the trip. Major hotels in Hua Hin/bkk have buses running between and it s relatively easy to catch a ride, and their are other commercial bus companies as well. Driving/traffic is such a pain it's worth looking at the alternatives
My concerns would be if you move your residence and the Sh*t hits the fan sometimes in the future,and you need to return in a hurry for whatever reason the last thing you need is a bureaucrat tell you no you can't enter, your not a resident!!
Have to agree with others, a friend got a job, flew up to organise accommodation came back shipped of his stuff. Got hit with more taxes than the goods were worth, as the goods weren't on the way when he flew in the first time. And the goods were purely house content.
Even if you have an expired Myanmar Passport have you tried to get it renewed in Canberra, and you will get better help from the Thai consulate in Sydney, as most of the Thai staff there are Aussie residents and so much more aware of day-to-day stuff, whereas Canberra seems to be Thais on a posting from Bkk.