It's my pleasure. I love all my frogs, but my darts are my favorites (i don't want the other ones hearing this though).
Springtails wont be enough for your thumbs. You will need to feed them fruit flies, and for thumbs, it will be D. melanogaster (here's a great thread for Fruit Flies cultures:
http://www.frogforum.net/care-articl...rosophila.html). As for springtails, here's another great question that Poison Beauties could answer (he's been very helpful with me when I started, and most of what I know comes from him). And to quote Michael: Temperate or Tropical they all thrive under the same conditions. So both should be fine. I use the temperate ones.
As for the gravel, Frog Forum's founder John made a viv last year for his P. terribilis (can't wait to have mine) that used small gravel and it seems to be fine. You'll find the pictures here:
http://www.frogforum.net/vivarium-te...terrarium.html.