Adri,
You made a super enclosure
You have made a super choice on the frog species also! They will NEVER hide.

As you continue your build, and if you have made a final decision on the terribilis, they will want some open space right on the substrate floor.
They love to hang- out.

You might want to look into bean beetle cultures ( when they are adults - they love these as an occasional treat). There easy to culture. A great occasional food supplement. They are big eaters ! 8 is a lot though ?

Your "build instructor" has taught you to layer the bottom of your enclosure ( gravel > batting > screening ) they way I make all of mine as well. Once you get more water in there , and the batting is touching the water, you can give that entire front portion of the substrate a good press. Eventually the bating and screening will disappear.

It looks great !