Arguably, the collapse of Credit Anstalt was a product of the tariffs, given that European Nations started to put up tariffs even before Smoot Hawley was ratified. 

You would expect a collapsing economy to import less, so the trade balance gives a distorted picture - better to look at total trade. More importantly, given how much investment was going into manufacturing in anticipation of increased manufacturing exports, the knock on effects to the rest of the economy were huge - hence the Letter of 1000 Economists, and Henry Ford virtually camping out at the white house.

But you are right, tightening of an already tight monetary policy into the crisis turned it into a depression