I cannot recommend varanustalk.com and savannahmonitor.net enough!!!

Your basking temps seem good enough for now. Between 120 and 150 is a good range(mine are at 140). The bulbs you should be using are called outdoor flood lights, and theyre way cheaper than anything at a pet store (most of the supplies for this guy, you will probably get at a hardware store) they are VERY important cuz the heat a large area without burning the lizard (like spotlights and heat emitters do) and they dont kill the humidity. you will find more info at varanustalk.

Humidity should be around 60% above ground and near 100%underground (it will help when you have a bigger enclosure with more substrate). If you are having trouble holding humidity, cover the lid with tin foil. You said something about how much dirt to use? As much as you can!!! In your aquarium, fill it more than half way with dirt. The minimum for an adult is 2 feet. They will use ALL of it. It might bump up the basking temps too.

For food, i really recomend worms, idk why but savs dont like crickets as much in my experience. Also, START TONG FEEDING, tongs are your best friends. Read the "taming" page on varanustalk about this.