I think if the hide was sawed in halves it would fit perfectly in the tank. Having moss or not has always been debatable. Personally I have had no problem with moss being in the tank if care and attention are taken. Ideally the moss would be much safer if the frog is tong-trained which reduces unintentional ingestion. The substrate should be moist, but not overly wet that it's soggy. Gibson is right about having drainage layer helps maintaining substrate moisture. Dumping some water would be ok as long as the substrate isn't overly wet (it promotes unwanted bacterial growth) since you have a nice drainage layer.