Good quote.

But I would have bolded

already familiar with applied mathematics ... where inference is needed

That's where Jaynes shines. Many mathematical subjects are treated axiomatically. Jaynes instead starts from the basic problem of representing uncertainty. Churning out the implications of axioms is a very different mindset than "I have data, what can I conclude from it?"

I think this is true as well.

A previous acquaintance with probability and statistics is not necessary; indeed, a certain amount of innocence in this area may be desirable, because there will be less to unlearn.