I'll comment on some of this:
The Turretin-Fulford argument has the same problem. At best it would show that certain specific writings (such as those associated with Moses and the apostles) are divinely inspired. It would not tell us whether or not other books are scriptural. And, crucially, it certainly would not show that scripture itself tells us which books are scriptural.
It's unclear what Feser is trying to say. Does he think Scripture doesn't contain self-referential statements about its contents and inspiration?
Now, sola scriptura tells us that scripture alone suffices to tell us what we need to know in matters of faith and morals. Well, the question of whether a certain book is scriptural is itself certainly a matter of faith and morals.
That's just a semantic ploy.
But the Turretin-Fulford argument, in making use of historical evidence, criteria for evaluating such evidence, general logical principles, etc. -- evidence, criteria, and principles which cannot themselves be found in scripture -- in order to settle this matter, thereby violates sola scriptura in the very act of defending it. For it uses extra-scriptural information and principles in order to settle a matter of faith and morals. In other words, it does precisely what the Jesuit point (a) cited by Feyerabend says a defender of sola scriptura implicitly has to do. So how exactly does the Turretin-Fulford argument constitute even a prima facie answer to point (a), or show that (a) is aimed at a “caricature”?
Feser fails to explain how those criteria cannot themselves be found in scripture. He merely asserts that to be the case.
Notice that I am not denying that the specific writings the Turretin-Fulford argument makes reference to are divinely inspired. I think they are divinely inspired. But I think that in arguing for their divine inspiration, it is a mistake to start with scripture itself. Rather, what comes first in the order of apologetics is an argument for the necessity of an infallible and authoritative institutional Church. We know that such-and-such purportedly scriptural writings are in fact infallible and authoritative only if we first know that there is an infallible and authoritative institutional Church, and that this Church has herself judged those writings to be infallible and authoritative. As St. Augustine wrote, “I would not believe the Gospel unless the authority of the Catholic Church moved me.”
i) How does one establish "necessity of an infallible and authoritative institutional Church" apart from the testimony of Scripture? He doesn't say.
ii) Moreover, that just pushes the same issue back a step. If you can't start with scripture, how can you start with "the Church"? How do we "know that there is an infallible and authoritative institutional Church"?