The amount of honey you get will depend on how full the cells are, but also how much the bees have drawn out the frame faces. With repeated use, several people have noticed that they get more honey per frame with subsequent harvests, and it seems likely that this is because the bees are drawing out the frames more and minimizing the beespace between frame faces.
Long story short, you may get around 2.5kg per frame the first time, but later harvests you should get 3kg or more.
You might find it helpful to invest in a cheap honey refractometer from eBay. They are around $30 to $50. Then you can test the honey to make sure it is ripe. If it isn't 18% water or less, just store in the freezer and use it within a month or two of defrosting. You can't legally sell it as honey if it isn't 18% or less, but it is perfectly safe to eat, just more likely to ferment.