Going off of the Intel era, Apple has typically provided seven years of software upgrades and two years of support for each OS upgrade - or in other words up to nine years total of software support. Hardware support exists on a comparable seven years based on the final sale date of a device.
Under a normal load, an M-series chip is around 15-30°C cooler than an Intel Mac with a fan. Unless you are redlining your CPU every single day (in which case an Air is probably not for you) this will not be an issue. M series chips will also be more resistant to thermal paste decay owing to their lower temperatures.
I run very comparable workloads to you on my Air and I rarely see my CPU tick above 40°C under load. My 2012 Mac mini idled at 65°C by comparison.