"Where does St. Chrysostom teach about that, in the Homilies on Matthew?"
Yes, and it is interesting that he gives such an explicitly simple explication about "daily bread" with nary a mention of the Eucharist. Even St. Theophylact, as I pointed out, only mentions it in passing and as an afterthought, and in the commentary on Luke, doesn't mention it at all.
Liddel and Scott traces the etymology in a way that doesn't link this word to "ousia" at all, and also cites Origen's reference to it as being a word that was rare, at best.
It is definitely valid translation of epiousios as "necessary for existence", as well as "of transcendant existence". What happens here is that the pedestrian meaning becomes the dictionary meaning, while the outworldly mystical connotation becomes secondary. The exact same thing happens in Russian, "suschnost" being "essence" but "nasuschny" commonly is understood as "vitally necessary".