8GB of RAM on a MAcbook AIr enough?

It's enough. The M series Macs use memory far more efficiently than the Intel series did, so a one-to-one comparison is of limited value.

Having said that it's always a good idea to purchase a Mac configured for how you expect to use it years from now, not just for today. There will be future needs impossible to anticipate, and getting more memory than you need right now will guarantee a long service life. Bear in mind you got nearly a decade of use out of your present Mac. How much is a few hundred dollars spread out over the course of a decade? Not much.

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My 2011 MacBook Air still works flawlessly. It was configured it to its limits at the time (4 GB).