If you plan on keeping it as pet for its whole life then keeping it at one temperature year round is perfectly fine. What are you feeding it? I personally wouldn't let any earthworms loose in the tank. I usually cut each worm in half and then throw the 2 pieces in front of a salamander and if it doesn't eat them after a while (but they always do) then take them out. Any crickets you put in there can run loose as long as you don't put in a whole bunch. Your salamander may also like dirt or bed-a-beast as substrate, but not peat moss. Bottled water is ok as long as it is spring water. Dechlorinated tap water is cheaper.