Neil, the only aspect of your questions I am competent to answer is #3 on carrying a camera in Thailand. No problem. I have done it often and there has never been an issue with any one, any where, except for one ultra-modern shopping center in downtown Bangkok where a security guard told me it was not allowed to take pictures inside - search me why. In Bangkok, the street vendors selling food and flowers are particularly colourful and interesting; once requested they never hesitated to allow me to take pictures of them and their "operations", and they didn't pose - they just went about their business. In some parts of town it is simply too busy and congested for anyone to pay any attention to what you are doing. Language is an issue there, but one manages to communicate somehow. As for subject matter in urban and rural Thailand - it is quite vast, between people shots, landscapes and cultural attractions. Your first trip will probably not be your last. Enjoy.
BTW, I don't know how you plan to fly there - I think I've tried most combos available and find that Air Canada or Cathay Pacific direct to Hong Kong, then connecting on Cathay to BKK is hands-down the fastest, most convenient routing. When you emerge from the airport building in BKK, if you are planning to go downtown, head for the public tax stand - the line moves quickly, and they are metered, air-conditioned, cheap and efficient. Tell the driver you want the tollway and you pay 60 Baht in tolls - well worth it!