For what it's worth, questions about very specific combinations of words can often be answered with Google search, as long as you remember to use quotes to force an exact match.
A search for にこそ returns >14 million results, while a search for こそに returns about 86k and a large number of them are cases where
こそ itself is being talked about, like dictionary entries. As a bonus, I can find one translated example sentence for にこそ and none for こそに. Given all this, I think we can safely say it's
にこそ in most cases.
I'd like to know which of the following is/are correct:
To be frank these all look weird to me -
自分に驚かされる is not very idiomatic. Also, this would probably be clearer if you used a
彼 to make it clear you were contrasting possibilities for the indirect object. You probably want something like: