First thing is advice from The Hitch Hikers Guide to The Galaxy: DON'T PANIC!
These cards are quite robust and 80C is not a problem, over time it will creep up and the fans/s will run faster, this is normal and just indicates a little dust build up on the cooler, again, nothing to worry about and easily cured by a quick clean. In fact if you have several pets in the house or live somewhere dusty, you should clean the card and CPU cooler, every 6 months or so, there is plenty of Youtube videos on how to do this and it's not hard.
Don't get worried about GPU usage, they are DESIGNED to run at 100% use. For years.
It's actually better to run the system 24/7 rather than turning it on and off-sounds odd I know but industrial systems run for decades like this and it's because of metal fatigue: As the system warms up it expands, stressing the solder joints on the card, then it cools when you turn it off and everything contracts. After thousands of heat up/cool down cycles the joins become brittle and ultimately break but the key is THOUSANDS of cycles-many YEARS of day-to-day use.
In short: Don't overclock.
Clean it out every 6 months or so.
If it has two or more fans, check they are actually working every month or so, sometimes one can fail and the drivers or your monitoring software will not pick it up.
You can leave the system running 24/7 if you wish to make it last a little longer but don't bother.
Don't panic if the temps/fanspeeds rise a little, it's perfectly normal and I wouldn't get even remotely concerned if my card was running at 85C (although I'd give it a clean fairly quickly).
Despite the massive abuse I've inflicted on my cards over the years I've not once had one fail on me.
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