Are you familiar with the nitrification cycle? You can get the run down with lots of important information and links for additional articles in the getting started thread link below in my signature.
are adorable. They don't have very good sight and will eat whatever they can fit in their mouths but are not what people would consider aggressive. They just eat what they can get.
You would be best to have a cycled tank small internal filter will work, and it takes awhile to get a tank cycled.
You can link from the below article about step over to the darkside - Talks about Fish In cycle. since you already have the frogs.
They can breed together, someone here got tadpoles! The male frog makes an odd noise and it is his croaking you can check for a youtube video to hear it, quite odd and not exactly a typical frog croaking noise!!!
They can be injured by too much ammonia which is from waste and degraded left over food. Water must be kept in a safe level. A liquid master test kit would be advisable.
You could have a small number I will have to check what size your tank is in Gallons - US. to give a better number for you. Also if the tank is cycled and how much of a water change schedule you can keep.