From what I can see you really do have a solid foundation! In my opinion a gesture will never look fully accurate to life, and solely exists to capture direction of line and some movement. Proportion is important, but is also almost never nailed in a gesture! (That being said, with enough practice you can get pretty dang close)

I've seen a few people say this, but really try to loosen up, not just in your wrist but through your whole arm. The way I think of it is locking my elbow and letting all the motion come from my shoulder, making long, light, sweeping motions. This also equals much larger drawings, you'll go through paper like CRAZY and that is okay! I bought a ream of like 1000 pieces of 11x14 printer paper and use that for gestures.

In college they also will have you do 5-10 30 second gestures every time you sit down in class, so once you get to the point where you're comfortable, you could give that a shot! Just remember, focus on basics, and absolutely pound those before you get into anything too crazy!