most people recommend the lowest grade gas (cheap stuff).
i think i used 32:1 that was marked on the bottle of oil for my mixture.

the vent line should just vent to the outside air. its basically so you dont get a vaccum in the tank and crush it by the carb pressure. ive seen these little walbros squish a tank flat..haha. on my engines i curve it up a little to keep fuel from siphoning out and then curve back to the bottom of the plane to exit.