Where in Thailand are you going? Thailands quite different depending where you are, particularly the North/Bangkok/South divide.
1. They do sell some traditional Chinese medicine, but nowhere near what you will find in China, so if that's what your after, take some with you. In general most medicine in Thailand is Western style and to a much higher standard than you will usually find in China. Virtually all Thai doctors I have talked to spoke good english as I believe they are trained to be doctors in English. As your English appears to be quite good you shouldn't have a problem. Although the same doesn't apply to pharmacy staff. Mosquito's sometimes carry tropical diseases in Thailand (dengue, malaria etc), but the best way to avoid these is to ensure you don't go out or cover up an hour either side of sunrise and sunset. Wear long pants/long sleeve shirts etc at these times. Also sleep with a mosquito net if you are in rural areas particularly. I don't recommend anti-malaria etc for Thailand as its not as high risk as some of its neighbours and they have horrible side effects.
2. Depending on where you are in Thailand, but most of Thailand is fairly tropical (except in the North). There are usually more animals in the forest in Thailand (big insects, scorpions, spiders, elephants, lots of monkeys etc) so be careful where you are. The best places usually for hiking are the national parks, but the entry fees can be expensive. My advice would be to add on to a tour group if you want to hike there first, then later go by yourself when you know the risks more and know where to go. Generally watch out for dogs in Thailand which can be aggressive and sometimes carry rabies. If you are hiking a lot, it might be a good idea to get the rabies immunisations before you go. Rabies is a fatal disease transmitted by blood and saliva from infected monkeys, dogs and some other animals. If you get bitten by a dog or monkey, get to a doctor and ensure you have the rabies injections to ensure you don't contract it (it's got a 99.999% kill rate).
3. Generally drink bottled water.
4. Not sure I can answer that question, there was a thread recently that suggested your UnionPay chinese card is usable throughout Thailand (which means you can withdraw Thai baht from ATMs in Thailand from your Chinese account, the bank will charge you to do so), but check with your bank on if that's possible and what their fees are for doing that.
5. The Thai people are much friendlier, in general, than Chinese people. They have a very different culture based mainly around buddhist principles, are much more likely to help people they don't know and are very welcoming and respectful. Public displays of emotion are very unusual as are any public displays of affection. Thai people pride themselves on being very smiley and happy on the outside, even though underneath they may be angry/upset/crazy. This very even faced attitude while nice initially can sometimes be annoying as they often never say what they mean. Many young people, especially in the North, speak or are learning Chinese and/or English, so as a young woman you shouldn't find it too hard to communicate or make friends, but learning some Thai language is a must still. In Thailand always be respectful to buddhist monks as they are a lot more genuinely buddhist than most Chinese buddhist monks (i.e. they have no possessions and have no cares about money etc, they seek enlightenment). This means never pointing your feet at buddhas in Temples, bowing and giving prayer hands to monks etc, you will see what I mean. Temples are everywhere so its hard to avoid buddhism :-). Being gay/transexual/transgender in Thailand is absolutely fine, there is no loss of face and its virtually encouraged. Lady boys are everywhere and they are generally nice open liberal minded people.
6. In general, Thailand is a very safe country, but always be careful walking late at night etc (applies to everywhere) particularly as a woman, this will also be frowned on and people may think you are a prostitute. Drugs are much more apparent in Thailand, but the penalties are just as harsh as China generally - keep away. I find I can spot dodgy looking Thai people a lot better than I can spot dodgy looking Chinese people, will be interesting to see if you find the same. You will find that Thailand is a big sex destination for bad Western men (its more apparent depending where you are), so don't be shocked when you see naughty westerners with young Thai ladies/lady boys - just a heads-up. This culture can cause a lot of alcohol/drug related crime and criminal groups so be careful around those areas.
Otherwise though, have a good time! Thailand is a beautiful country with beautiful people, great food and an awesome culture. I have never heard anyone come back from Thailand and say they didn't enjoy themselves (including a few Chinese people), so I am sure you will have a blast!