1. I also think it is 石龍.
2. 一道橋 has a literary feel. We usually write and say 一條橋.
3. If 啦 is pronounced laa1, it means "Drive off!" Somebody must be yelling at the driver. If 啦 is pronounced laa3, in which case I would write 喇, then it means "The car is driving off". Depending on the context, somebody is either happy or sad to see that the car is driving off.
4. This is just the opposite of (3). I agree with what KaChon said about the three possibilities of interpretation. Regarding the grammar, yes, sometime it's illogical. It's like 落雨啦(It's raining). 落 means "fall". 雨 means "rain". Then why don't we say 雨落啦? We just don't say it that way. I think you can only memorize them as fixed expressions. It is not that you can place any verb before any subject, though.
5. Your interpretation of 就 is correct and adding 一 would sound better, but the difference is not very big. However, I would like to highlight that 起手 meaning to start is very old fashioned (as usual, I mean in Hong Kong). We would say 開始 instead. In your example, I would say 佢一開口我就知佢係外國人 instead. 開口 means to start speaking (literally, open the mouth).
6. Have you heard of the saying 無三不成幾(If the quantity is less than three, it cannot be described as several)? Although this is not the hard and fast criteria, you can interpret 六十幾 as somewhere between 64 and 69. Instead, 六十零(leng4) is closer to 60, probably 61 to 63.