You should invest in a "temp gun". Pro -exotics sells them. Theres a link to their site at the top of the monitor forum page.
You need to have a really hot basking area. Were talking over 120 degrees! Give him hiding spots on both the hot and cool sides. Start introducing mice to him asap. Dont worry too much about full spectrum this and that. Just get him some heat, asap. Hes not an Iguana.
Also, ditch the bark, and go dig up some nice dirt. Hell love it. He can dig and burrow and be a dirty little monitor.
As far as temperment...hes gonna most likely be a jerk. Be prepared to have a huge monster on your hands. Youre gonna need to build a bigger enclosure in the near future. 8' X 4' at least. I hope youre not squirmish when it comes to mice, rats and bloody messes. Every once in a while even a Nile will get the urge to rip a rodent to shreds. Thats a LOVELY smell to come home to. Rat guts baking under the emmitter.
Your cute little Nile is a BIG commitment. I really hope you can step to the plate with this one. What Ive told you is just the tip of the iceburg. Youve got lots more instore for you.
What I really reccomend is that people take the time to research BEFORE buying that baby Nile or Bosc. You have just given that petshop owner more reason to buy more wild Caught little babies. They should not even be on the market. There are PLENTY of captive bred animals that make much better "pets". You cant go back now though. Youve got a kid to raise. Treat it as such.
Good luck to you and your new baby.
Rgrds,
Michelle