The stick-on thermometers are not really reliable, I wouldn't trust it at all. A digital thermometer with a probe is much more reliable, and can be found at Walmart for about $12. The glass traps the heat inside the tank, which is why it's not recommended to use glass tanks outside. If it gets too hot, he has no where to go. I would at least get the tank out of the sun ASAP.
Since you have other reptiles, definitely quarantine him by keeping him in a different room than the others, as you don't want him spreading any mites or other parasites or illnesses to them.
The only ways to tell if it's male or female are to have an experienced vet or expert "pop" or probe him/her. You can't tell just by looking at them. They can easily get up to 4 feet long, and around 1500-2000 grams (that's just an estimate, they can be larger or smaller, and females tend to be a bit bigger). He should be fine in the 40 gallon breeder for his entire life.