The concept of free will doesn't make sense, so the proposition of its truth turns out to be self-evidently wrong after a certain amont of thought.
It does make sense to Daniel Dennett and Sam Harris, who have both given it more than "a certain amount of thought".
I think that's all that need be said here.
Not true- Sam Harris concludes it's incoherent. That's at the VERY START of what you linked to.
I've raised arguments for philosophical scepticism before, which have mostly been argued against in a Popper-esque manner of arguing that even if we don't know anything with certainty, we can have legitimate knowledge on probabilities.
The problem with this, however, is how you answer a sceptic about the notion of probability having a correlation with reality. Probability depends upon axioms of probability- how are said axioms to be justified? It can't be by definition, or it has no correlation to reality.