Heating and lighting in house gecko tank.. ?

Hey, I've just made a tank for a little house gecko i found hes about 10 cm long, The tanks Is 20 cm long and about 15 cm wide.. I have dirt from my backyard in there, and sponges underneath it to keep the humidity right, i have bark that hes hiding in, and a light thats about 5 - 6 watts, it gets warm, its 2:40 pm now, if i leave that on for a few hours, the tank will heat up, it has a plastic guard thing around the bulb and i coloured it in red, the plastic around the light is warm and its been on for about 20 mins, so Is that ok for lighting AND heating? And is the tank too small? Im in australia, and i want to know why you need lights and stuff, when the geckos warm up just throughout the day, Why do you need to provide heat if they get it from the wild and they can do that in a tank? I have small crickets, i bought them today, how often, and when should i feed him (At night? or put them in and let them run around?) Hes shedding his skin aswell, it'd be good if you could help me. Thanks :D Oh and im only 14 so dont be all like ''wow your retarded look at the way you talk'' and stuff', cause i dont care. :) Kthanxbai.