In terms of the WashU cons, you don’t have to stay in MO after graduation (most students don’t and there are alumni networks in every major American city). You might hear a tornado siren test, but you’d be EXTREMELY unlikely to encounter issues with an actual tornado.
IAS at Wash U is basically International Relations, just with a different name. They also have an Int. Business minor that is fairly popular to pair with IAS. Wash U is also very strong in psych., which you did mention.
If you’re worried about going far from home, I do think WashU does a great job of trying to prevent homesickness. There’s a lot of resources and they can even pair you with St. Louis families for a homecooked meal.