We recommend buying several thousand in different sizes from mini up to large so that you will have worms at all different stages of their life cycle at any given moment. We also recommend keeping them in shallow trays as opposed to aquariums because they need to be kept shallow with lots of surface area. You can either use large unused cat boxes or trays you find at Home Depot or Lowe's. They must be kept at a depth of no more than 1.5" and have their droppings (castings) sifted out every 2-3 days. You can do this with a large flour sifter (the semi-circle type with a handle). And sift the worms from one bin into another. When you have beetles who have laid eggs, though you must stop sifting or you will lose your eggs as well.
Our regular mealworms will very readily pupate and become beetles that lay eggs. We sell several species of worm, please be sure to purchase our regular mealworms found on this page: Mealworms
For the home breeder, we recommend using the good instructions found on either of these two websites: Raising Mealworms for Bluebirds Happy Chicken Coop