I have a Pakistani-American friend from high-school, who's from TX (Sugarland) who was in the same boat as you. He wanted to do medicine but was a bit irked at the four-year Bachelor's requirement in North America. He has a sister who's also an AKU alumni and is now a resident in NY, so that somewhat influenced his decision.
His equivalence certificate took around three days of running in and around the IBCC office in Islamabad; it wasn't very difficult. Just be sure that all your paperwork is in order.
Because of the fact that the AKU academic year begins a bit later than the usual August/September mould, he actually enrolled in UT Austin for a semester just as a safety net while his AKU application was being processed.
As for AKU itself, he's been enjoying his time there. Karachi is a large city and like most countries, if you're reasonably healthy financially it's akin to a playground. The university itself, and your entering batch will be composed of academic stalwarts mostly from Lyceum/KGS but also a few foreign-raised Pakistanis such as himself. The environment is fast-paced but at a school like AKU you're given the resources necessary to achieve as you will. I'm not sure of your exact background but seeing as we'd been through that annoying rigor of AP Chemistry/Physics/Biology he was more than prepared.
As for the social crowd, again, most AKU students come from well-to-do families (not sure how else to phrase this) so it's a relatively normal vibe. There're plenty of extra-curricular events happening weekly in both a medical and leisurely context so I doubt it's a dead campus or anything. That being said, it's extremely academically-orientated. Most students are gunners because that's what's required. You either need to strap in or face getting left behind.