MacBook Air 2018 user here. Moving from a Mac pro 2012 (which in its fine right it was pretty bulky and heavy). So the move was a good one. Anyway, the laptop itself is a great little thing; very light, easy to carry around, and put into laptop bags. Reliable (so far), although the charger cable is beginning to go, 2 years in.
I generally tend to run different softwares on mine at the same time, and also run windows 10 on my mac Air via parallel. And I've yet noticed mine heating up, or making any noise from the fans, etc.
The only thing I'll fault my mac air is the keyboard. They sometimes can become a bit stiff (feeling as though there may be some dirt trapped beneath them). So some keys may become a bit hard to press. Although mine only does this with either the space key or the 0. Other than this, the keyboard is fine (although it does make a small amount of noise).
Other than that, theyre great little machines - I love mine to the bit. Actually thinking of upgrading the 2020 version (just to stay up to date).