1. Yes. Getting into Andover you need to pass the whole application process. Getting into BL, you only need your school GPA and SSAT/ISEE. So BL has more nerds. Getting into Newton high, as long as you rent an apartment or buy a house there, everybody can get in. So you know the difference.
2. A lot of people choose boarding if you do not live in Andover. But the kids must be mature enough to take care of him/herself on everything, academically, socially, etc..
3. Before 2010, it is about 20%, 2010 is ~15%. More and more Asian kids start to apply, but not every kid goes there even if he/her got in. All my friends' S or D could not get into Andover, not because of academic scores, but more because of no other shinning spot.
4. Getting in Andover is just first step, you'd better make sure your D can continue standing out if she wants to go to IVY.