I think the geographical location did affect China, Korea, and Japan. The location made it easier to trade between the three. Such as silk, brocades, cotton, tea, books, copper coins, porcelain, swords, folding fans, sulfur, copper, silver, etc.
The geographic locations of Japan,China, and Korea did contribute to the trade because they are close enough to trade yet not close enough to easily make or collect the stuff themselves. They traded things that they specialized in that the other country did not have or were good at.
The people in those countries were able to elevate their standard of living. Since trade was so prevalent people were able to advance technology ,find new routes, and make money due to demand.
No i do not think that trade was not instrumental in spread of Buddhism because they remained peaceful throughout the years and when religion spreads violence follows
