I raise a lot of worms. My fishing worms mainly come from two 4'x4' beds that are about 10" high. The bottoms are lined with landscaping cloth.
This old thread has quite a bit of info:
I'm not a redworm murderer Redworms grow the fasted when kept well fed. European nightcrawlers will do reasonably well, and are a little larger than red worms. When you buy fishing worms in cartons, you are generally getting one or the other. Canadian night crawlers won't reproduce and can't take summer heat in a bed.
You can buy bulk worms by the pound. Just search for red worms. But, red worms reproduce fast. Four or five cartons of 50 "fishing worms" will get you started.
The beds should be out of direct sunlight where they can overheat and die. They need food, and they need moisture.
My worms work for a living. I usually always have a number of very large compost piles that I turn with the loader on my tractor. I've also got two compost "tumblers". All get "seeded" with worms. We also have a number of raised beds and containers outside the backdoor. When we renew them for new plantings, they each get a handful of worms.
Good luck,
Ken