You probably dont even need to get any worms. They will find the great soil you've mixed, make it their home and multiply. If you were creating a worm bin, or some sort of bed that had no direct contact with the regular soil, then I'd say consider getting them, but with what you have described, you shouldnt need to add worms. I started my current veggie garden several years ago. The worms quickly found the compost, hay and leaves and multiplied. My compost bin is the same way. last year when i started removing finished compost from it, there were tons of red worms in it. I was so surprised, but excited too, to see I was doing it right!..