And while the Turkish have far more firepower and air power than Kurds, the terrain is extremely favourable for a defending force, particularly when it is as motivated and well-trained as the Kurdish fighters. A Turkish attack can become a debacle, or at militarily "best", a massacre of civilian population resulting in further alienating Turkey from civilization.
Don't misunderstand that I think this is a) a good idea, or b) ultimately going to work out the way Turkey wants it to work out.
I don't think the kurds will choose to live and die by Afrin.
Is it even "likely" that you can shoot down a jet with an manually operated anti aircraft gun? Sure it's "possible"
Does Turkey have guided bombs? And will they be re-supplied so that Turkish air force could use them at will?