The truth is it’s not that important how many worms you start with if you’re willing to be patient. As long as there’s food and space, your worms will fill your bin in time.
Personally, I would rather start with less worms and let them fill the bin then to start with too many both because it’s cheaper and there’s less chance of things going wrong, see Escaping Worms.
Starting with fewer worms just means you need to be a bit more attentive. Check on the bin to see if things are composting every 2-3 days. Cut back on food or add more food depending on how it’s going. Chop large pieces of food smaller so it’s easier for the worms to digest. Make sure there’s some form of grit to help the worms digest their food. I like egg shells but you can also use sand. Allow the worms to breakdown the majority of the food before adding more.
Don’t worry, your worms will eventually fill the bin. 🙂
Also it’s better to start with worms and compost from their original habit. I always give worms with their original compost so the worms aren’t just put into a new environment.