Does the "let them cry" method work? On a 4mo old? We r going from swing to crib. Need good tips. Slow transition? Soothe? Let cry?

They train you. If they're crying, it means that they want something from you. If you give it to them, then they learn that crying = getting something. If you don't give it to them, then they learn the opposite. This is not to say that you withhold diaper changes and feeding. However, learning to self-sooth is an important step in a kiddo's development.
Many answers. I generally recommend that you have to learn how to raise your child, and they are all different. That said, if you smother them every time they cry, eventually it will get to the point you want to go out, or even to the bathroom, and the child simply cries all while you are gone, because "mommy is not there". I would let a child cry, it will teach them independence.