The tank can support a few inches of water. But if you are worried about it leaking then you can just apply some aquarium safe silicone to the edges to create a tighter seal.
The substrate is much too wet. That kind of environment promotes bacterial and fungal growth. And since you have no drainage layer the water on the bottom will become very unclean and unsafe rather quickly.
Moss is an impaction risk as stated before.
There should be more places to get out of the light. If all three are in the log at once it can be stressful.
Otherwise
the tank looks good 