I've had tomatoes in the past and I have one right now who is doing really well. I keep her tank in the mid 70s range and give her lots of burrowing room as that is her favorite thing to do besides eat. Keep the humidity high. I love your little tomato such a cutie. His/her colors should change more as s/he gets older. Tomatoes are known for the ferrous appetite and hopefully your tomato carries this trait. As for substrate you could use paper towel just make sure you clean it out everyday and you could also use coco-fiber. Since your frog is so small just put a half-inch or so of the fiber down. Your tank right now looks very nice just try to get those temperatures in the mid to high 70s. A little temperature drop at night and you and your little tomato should be fine. Hope this helps if you have any questions or concerns feel free to message me. Glad to see other Tomato keepers out there