I have been wearing cardigans (mostly from American Apparel) for a while now, and I have a couple questions: 1. What is the appropriate length for a slim-fitting cardigan worn with slim-fitting slacks or jeans? How much below the belt should it go? 2. Is it ok or even stylish to have a collared shirt peeking out from the bottom of it, or should any shirts worn under the cardigan be tucked in?