Well, you would have to determine what TEMP the huge is reading. Air temp or oil temp? If its air temp, then you would need to determine what temperature the gauge is set to warn on. I'm unfamiliar with any consistent air/engine temperature that would be used to declare the engine is HOT.
For oil temp, (and you should be able to locate an electronic OIL TEMP sensor as it would be quite large) the same would be true as above (what TEMP did they set as normal vs high?) Im afraid only the previous owner who installed this instrument could answer those questions. My suggestion, IGNORE it and disable it as its most likely very unreliable as valid input.
As to your idling issues, were you using the choke? These bikes prefer a bit of choke for a few minutes then fully shut the choke off and ride on. If you allow these bikes to idle away in the driveway/garage, they do get quite hot as they're air-cooled and need flowing air over the engine to keep them cool. You could have debris in the tank, slightly clogged carbs, a clogged fuel filter, etc.
Can you take some close-up pictures of your bike? Start on the left side, shoot a clear picture of the carbs from about 1-2' away. Then same from the opposite side. Show us the gauge too. Shoot pictures of the right side of the motor (this should capture the head to foot peg) and repeat on the left side. You might prefer to use a PhotoBucket or Flickr account to paste the image links.
You said this is your first bike, so deviations from stock will be readily noticeable by folks here long before they are to you. And since we can't see your bike, its difficult to diagnose any of your issues.