before you get 100 responses saying "it depends" a good "average" is about 10 ounces per plant outdoors. of course that is an "average" so it can vary greatly depending on strain, your growing skills, water, nutes etc etc etc. so you might actually get 5 grams or maybe 5 lbs.
not a huge fan of topping, i would get some fishing line and LST the plants so it gets optimal light.