The gudgeons/gobies are not aggressive at all. Everyone in the tank is pretty peaceful for the most part. The gourami will dart at fish every now and again, but from all I can tell, mostly keeps to himself.
The snails are in a 1.5 gallon jar right now. I'm going to keep them in there. Add a heater..filter. Something. They just get picked on too much with fish in the tank. The female Japan blue guppies picked at them relentlessly.