For substrate, I'd get some kind of coco fiber or something of the sort since they do like to get down in there. They shouldn't swallow it, they're not exactly ravenous eaters like a whites tree frog. My peepers rarely got something in their mouths while eating that they weren't supposed to, and when they did, it was a piece of leaf litter that they could "wipe" out of their mouths. If you're really concerned, you could dump the food in a bowl in the tank. A lot of them will be eaten before they ever make it out of the bowl. Especially since they will stop to clean vitamin dust off themselves.

I kept mine around 70 degrees also. I would get something to monitor the temps and humidity though, you might be surprised by how off it can get being a tank vs the open air and a light source on there. Plus, if there is ever an issue, then you have the exact temps and humidity on hand to see if that can be a contributing factor to any illnesses or strange behaviors.

I have a local pet store that sells fruit fly cultures, or you can purchase them online.