I really depends on how old/big your frogs are, but I recommend starting out with at least 1 pound of worms, (800-1200 worms), for setting up a new tub. Also give them some time to get established before you start feeding them out. Red Wrigglers will double their population every 90 days, and are probably the most prolific.

I colonize my worms in big rubbermaid/sterelite tubs, the bigger the better, but it shouldn't be so big that you can't handle it. Most of my worm tubs are set up in this size of tub, or a bit larger:
68L Rubbermaid Roughneck (Grey) (10 Pack) at Walmart.ca

I keep Red Wrigglers(3 tubs), European Nightcrawlers (2 tubs), and African Nightcrawlers (2 tubs). There are a few other species of composting worms that are easy to breed as well.
The Red Wrigglers are by far the easiest, and I recommend them first for the first worm colony.
I recommend setting up two tubs, just in case of an accident, you wouldn't want to crash your colony and be left with nothing.
Out of the three types of worms I keep, I'd say that the European Nightcrawlers gave me the most difficulties. I've crashed them twice.

For your dart frog, I'd recommend culturing Flightless Fruit Flies, or Bean Weevils, or something similar.