Yes. I survive off 700$ a month comfortably, and half of that is excessive spending. But i think it mostly depends how you eat, rent cost which i got lucky on 5k plus less than 1k electric and is nice place..
I have 2 passports. Law is, you must enter/exit the country on that country's passport (so if you are a citizen of Thailand, you are not supposed to enter or exit thailand on your Australian passport, and vice versa --> though i suppose it is possible to do so, i know someone who did but they were worried about the exit thereafter)..
but yes in regards to the ticket could be problematic. I would get the passport renewed, or call the airliner to see what to do.
I know a few languages, and thai grammar structure is quite simple but cannot compare to other languages, cannot use perfect tenses (have been, had been, will have been).
Keep in mind monthly house rentals (at least in koh phangan) have dramatically decreased. You can find a bungalow for 3000-8000 baht utilities included depending. Pretty cheap.