Is there written testimony in German by officers at the moment evaluating the Russians and concluding an invasion would it all likelihood be a cakewalk? How much overconfident in their ability/lack of on the other side, show in actual/factual period records?
The contempt for Slavs and Bolshevism was endemic in the German officer corps long before 1940, so I'd say that it didn't cause the overconfidence on its own. With that being said, however, the Winter War definitely increased their confidence of success, especially given how the Wehrmacht preformed against what was perceived to be the best army in the world a few months later. I'd say didn't cause Operation Barbarossa to be accepted, but it probably helped Hitler advance his arguments for it and reassure doubters. The Winter War's impact was far from limited to Germany-many Western observers expected the Wehrmacht to have an easy victory over the Soviet Union.
Keep in mind that the Finns were more Aryan looking than the Germans were: overwhelmingly tall, blue eyed, blonde haired, pale skinned people. The Winter War probably solidified Nazi racial propaganda as a result.