I used to run egts when I raced snocross. Very helpfull for tuning. I don't know if they are really worth it for trail riding. If you like to tune and are worried about frying a motor then it is great piece of mind. You can run egts with a single pipe. You put both sensors in the y pipe, one in each cylinder. Whatever unit you go with should tell you how far from the cylinder to mount the sensor. You can buy egts from just about any snowmobile catalog, ebay, and probably any dealer. hope this helps.
No one can really tell you that. Every sled is different. Your "hot-spot" will be in the mid range say 6-7000 rpm's. I would say temps will be in the 1200-1300 range at this point maybe hotter if you ride there too long.