With regard to ECs, do what is right for you. Whatever you do, do it well.
Also, you might want to read the “applying sideways” blog on the MIT admissions web site. While MIT is not on your list, the same approach is appropriate for other selective universities as well.
Yes. You grades will be interpreted in the context of the high school that you attend. Also, you do not need to be perfect (and 9 APs are plenty).
The eight Ivy League schools are not all the same. Figure out which ones are a good fit for you and why. This is likely to come across in your applications in one way or another.
If by “all Ivies” you are also thinking of other highly ranked schools such as Caltech, Chicago, MIT, and Stanford, please keep in mind that these are not in the Ivy League (although what Stanford is doing in the Atlantic Coast Conference might be even harder to explain).
To me it looks like you are doing very well and are likely to have some very good options.