Do you use a filter or just do a complete or partial water change? How often do you think I would need to clean out a 40 gal with maybe three or four fire bellied toads?

Do I need to make a false bottom( I dont want too get this complicated), I want to keep this simple but make it pretty at the same time.

Do I just treat them like I would fish? Meaning partial water changes once a week after cycling water the first time.
What kind of filter? I have two old fish filters, one was for a 20 gallon and one was for a 29 gallon but was rated for higher(the kind that fit on the side and suck up the water and spit it back out the top).I also have a submersible heater for a mid size tank).

Maybe someone would be so kind as to make a list of what I would need to outfit a 40 gallon for these little FBT's(I have a tank, with a screen lid).I like the idea of either river rock as substrate or sand but prefer the rock.
Will they eat baby dubia roaches and mealworms?