Well, in the wild they certainly will be feeding on leeches of different species and sizes, but I think it requires a bit of caution since larger leeches may be too much for the little ones to handle. The leeches may attach their suction cup to the mouth or other place on the newt and prevent it from swallowing properly. I think keeping the leeches separate from the newts and feeding them ones that are small enough for them would be a good idea. You can keep leeches in a bait bucket that has an aerator, though you'll need to change the water. Depending on the species, food varies from algae and plant material to decomposing materials to meat. Check in with the seller to find out the species.