100 worms isn't a lot, but if you have time, they will reproduce. I threw in barely a dozen worms in my worm bin and several months later it is full of thousands and thousands of worms. If you want to speed things up, you can always add more worms, of course.

The white mites should not be a problem. I have noticed that outdoors in the gravel beds the white mites just are not present. I have snails in my worm bed and many other critters. Perhaps one of them eats these mites or the conditions are not favorable to the white mites?

You sound like you are off to a great start. Keep it up, and keep us posted!