I only have African Clawed frogs so I can only help so much but here is what I can tell you.

For a 5 gallon with only a dwarf frog or two a sponge filter might be your best bet. They do need an air pump but they are cheap and easy to maintain. I have several as secondary filters in my tanks and they work great. Check ebay or amazon, the ones I have cost less than $5 and do the job.

For the clawed frogs a bare bottom, large river rock or fine sand is recommended substrate. Bare glass is easiest to clean but I don't like the way it looks. I tried river rock and it was very difficult to clean. Now I have natural play sand and it works well for me. It looks nice and is pretty easy to clean.

You will want to cycle the tank prior to adding the frogs. It basically involves getting bacterial to grow in the filter and tank that will break down ammonia into less dangerous nitrites and nitrates. A water test kit would be helpful or you can ask your local pet store if they can test it. That way you can avoid a dangerous ammonia spike. There are some additives that claim to avoid it but I've never tried any. Also make sure to use a water treatment to remove any chlorine from your water.

Good luck and make sure to post some pics once you have things settled.