1. It depends. If your kid is bright and at the top 25-50 in ivies, definitely go with ivies. The kid is going to have better peers. If the kid is at the bottom 50% then it's probably true just going to a lower school and get higher GPA. But remember, GPA from different schools and different classes is also considered;
2. GPA is extremely important. We we also have standardized test MCAT. As mentioned above, school is also important. From real world experience, if you graduated from a better college and everything else is equal, you will probably get more interviews for residency;
3. Yes, but you also lost the chance getting into better medical schools.
All in all, if the kid is bright, he/she doesn't have to worry about all those. If the kid is average, it's going to be tough no matter what.