want to adopt a child from China to the US, please advice

I am considering adopting a child in China. I have myown son at age of 5. Now my question is:

1. Is it better to adopt a son or a daughter for my family and for my son?
2. What age is the best for adopted child?
3. How to adopt a child from China? I want the child to be healthy, no any defects, as the minimum requirement. Further, try hard to get one smarter and more beautiful.

Please advice. Thanks a lot.