You can reuse rested soil but problem with it is after being outside for a while it's most likely contaminated with insects that can flourish in an indoor environment because the predatory bugs usually don't come along. Good soil is pretty cheap so why skimp on the dirt?

You can put out your plants as soon as the temps stay above 50f. Start them in full shade then gradually give them more direct sunlight over7-10 days and they'll be fine.

And do not put worms into your pots unless you're also planning on feeding them. They will turn on your roots if that is all the can find to eat.