The answer to your question of how to decide the quantity of earth worms to optimize your vermicomposting can be answered by two avenues do an extensive review of the literature and also do an experiment with defined initial populations of earth worms. The two avenues will allow you to develop the experiment thoughtfully and also give an answer which works under your exact conditions.
A good rule of thumb is one pound of worms per square feet of the bin being used. Another way to calculate it is one pound of worms per pound of food waste. There are roughly 1000 mature worms in a pound. But there are a lot of considerations that come into play when deciding how many red wigglers you need.For most average sized domestic worm bins, we would suggest you start with 1 lb. (approximately 800 - 1000) mixed sized worms. 1kg. (earthworms net weight, approximately 2000 young adults and baby worms, with 0.5g average weight).