Re: Idiom Frequency
My own opinion is that the more noticeable idioms are difficult for beginners to use actively in any language, because it is not easy to learn the contexts in which they are likely to occur without extensive exposure to the language.
Caricatures of "foreigners" in fiction, etc. often include a misuse of idioms – perhaps caricatures in your own first language too. Over-use of idioms can be another problem.
But I think if you concentrate on learning to recognise and understand idioms in newspapers, magazines, etc., you will also gradually learn the contexts in which they are used, and develop an ear for them. So I would take a realistic but not pessimistic view.
(Other members may have other opinions, of course!)
All the best,
Not a professional ESL teacher.