I will be interested to see what Dr. Krentz says in response to your query;
in addition to whatever he says, perhaps I could make a suggestion or two.
You might begin with the two documents related to Polycarp: his _Letter to
the Philippians_, and then _The Martyrdom of Polycarp._ The former will
remind you a great deal of some NT documents, while the latter tells an
interesting tale in a rather straightforward narrative style. Save the
_Epistle to Diognetus_ for last; it will be a nice bridge to secular
writers. The level of difficulty of the remaining documents doesn't vary
all that much; a more noticable difference is in the area of vocabulary
(e.g., 1 Clement uses a lot of Septuagintal terminology, while Ignatius uses
some secular phrases in rather idiomatic ways). The nice thing about doing
the AF is that the lexicons and grammars you already have will likely serve
quite well; indeed, BAGD includes all the vocab of the AF (though I find
myself disagreeing with their conclusions on some terms, for which LSJ is of
more help). Finally--and this is my main reason for the note--as an intro
to the AF, a nice little book has just been published this month: Clayton
Jefford et al., _Reading the Apostolic Fathers: An Introduction_
(Hendrickson, 1996). Though it will not help you with the Greek, it does
pack a great deal of introductory material about the AF into a very nice
format, and will give some context to what you read in the AF themselves.
Mike Holmes