The soil sounds fine, just make sure you switch it out about once a month. You can bring the tank humidity up to about 80%, I would recommend digital gauges if you don't have them, analog type are notoriously inaccurate.
My frog loved her water feature, but after losing her to what was most likely toxic water that looked very clean and was fresh and treated just three days prior, I highly recommend being diligent about the water and testing daily if you are going to have a water feature.