Reply from Agony Uncle
1. Flower vase & flower, a management handicraft (if done by yourself)
2. Clocks (it's taboo to give clock in Chinese), pets.
3. If you are buying as a group and contributing a sum of $50 would be normal.
If you are buying yourself, ie. it should be a closer friend a gift of $200 would be normal.
4. In Singapore given the heat it could be assumed safely to dress casual but then again a word of caution: do not dress in your shorts and vest unless it is stated to be pool-side in the invite. Also the food served may be a hint, eg. BBQ, buffet in club house would be casual, sit down dinner slightly more formal.