Hello and welcome to FF Sarah

! First thing to do is to read this article:
Frog Forum - Fire-Bellied Toad Care and Breeding - Bombina orientalis and relatives. Unless your room is colder than their temperature parameters, you do not need to heat the enclosure. Myself would be careful with an over rated aquarium water heater, since you will have only a fraction of the tanks volume with water.
If the sponge filter is running in tank and seeded with bacteria, you can introduce frogs right away and change 25% water volume weekly. If filter is new, then do 25% water change daily for the first month or until both ammonia and nitrites reach zero. If new tank, you can cycle in two weeks using Seachem Stability or similar product. Do not use products that reduce ammonia, they will make tank cycling take longer.
You can feed them earthworms (i.e. Canadian Night Crawlers); but need to cut them (from pointy end) to a size that will fit in their mouths. Crickets are good. Size should be same or smaller than distance between frogs eyes and at that size crickets might not be noisy yet. Gut load them with lettuce, carrots, and crushed cherios/oats. Do use food supplements, more info on that in here:
http://www.frogforum.net/food-feeder...schedules.html. Good luck

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