Put a layer on top of the peat and use coarse. It stops the frogs getting covered with substrate and gives the feeder insects places to hide and breed within the viv where the frogs are less likely to get at them.
Just rest the light on top of the lid. You can either rest it on the glass plates (as I do) or slide one forward a bit and rest it on the mesh. If you don't have one, a reflector (available at most herp or aquatic shops for a few £) will increase the light into the viv substantially.