I also think the air vents are way too smal but this can stop unwanted bugs so would please some people. Worm Farms are made up of many types of bugs which all help the decomposition process and are essential in a healthy farm. The tap on the bottom really is just a gimmick but essential if the bedding is too wet. Worm farms shouldn't drip moisture. The moisture is really only water sweated out of the bedding and picks up some nuitrients along the way. Worm urine wouldnt really add to the water draining out. Therefore it isn't really Worm Tea or Worm Pee, still if diluted is useful to feed your plants.
I don't understand why you would want 5 worm farms unless you were selling worms or using a huge amount of worm castings. Did any collapse from the weight? A school teacher mentioned to me that she had seen it happen and if not on level ground I can see it happening.
Stackable farms are more of a maketing gimmick, and a clever one because this is what people now expect. You would never see a worm breeder using one to raise worms but just open beds.