5) Extracurricular reading. This is probably THE major obstacle to learning Chinese for children of Chinese heritage (or anyone learning Chinese as second language really). One probably needs to know 1,000 to 2,000 characters to recognize about 85-98% of the characters used in the real world. The pace that typical CCH learns the characters in Chinese school is too slow, such that the children can not enjoy extracurricular reading by 10-12. In that case, which occurs almost all the time in the US, English takes over. We are able to overcome this only through biannual immersion and schooling trips to Taiwan and/or daily Chinese lessons (M-F) in the US early on, such that Charlotte, our elder daughter, can read junior novels comfortably without phonetics a few months before she turns 11. That came as BIG relief for us and the family celebrated big time! We expect Georgia, our bright younger daughter, to make that milestone by nine and a half, if not sooner.
6) Priority. There is only 24 hour a day. How each devote his/her time to acquiring new skills is different. I would rather that my daughters have superior Chinese (for a CCH) than becoming a typical accomplished pianist (or whatever it is that they pursue) when they leave for college.