Forgive me if I am making a generalisation, but most pilots are not trained in permit aircraft, but in 152s/PA28s and operate from licenced airfields.
To move straight into a D9 - light, under-powered, tailwheel etc and to fly it off a farm strip as well (who will be keeping an eye on him???) seems quite a leap.
If he is to undergo good tailwheel training, get farm strip experience with others etc etc, then there shouldn't be a problem as it is a forgiving beast
But to buy a plane, such as a D9, before completing a PPL - ie by definition, buying a plane he cannot know he is capable of flying - does not exactly sound sensible.
I just hope, for the Jodel's sake, he learns quickly, as there are a lot of nasty surprises waiting for him