what is the averge rainfall for the oceans?

Answer 1

Depends on what part of the ocean. For example, near the ITCZ (equator) it is high. Other areas can be very low.

Answer 2

Probably varies just like it does on land...for instance, Antarctia is the driest continent and is surrounded by ocean. Storm fronts don't suddenly turn off the rain when they hit land (unless forced upward by mountains). No doubt in the warmer regions of the world, the rainfall is substantial since you have heating by the sun, plenty of atmospheric moisture to work with and cold dry fronts moving in from either pole.