I am not aware of any gt-label requirement for taking the AP courses or applying for IB programmes. I am sure there are grade-level achievement requirements for AP. A student would have to get such and such grade in certain courses to sign up, but you probably are figuring on that.

Fairfax is very bustling and fun, Herndon is a bit more out in the country, but is a nice flourishing community with an historic downtown area, lots of decent restaurants and many large companies.