Therefore: What did the Early Church Fathers have to say about masturbation?
I don't have quotes, but I can throw my 2 cents in with an overview and some book suggestions. If you search for "contraception" on this forum you'll probably find a good bit of interesting reading which deal with your question (albeit in an indirect way). Here are three things that I'm pretty sure that most of the early fathers held to: 1) They considered lust bad (including lust for your wife, though I'm pretty sure many of them drew a distinction between lust and attraction, where the latter was acceptable); 2) They felt that sexual activity had to have some justification (procreation being the most common, then avoiding fornication, building a bond, producing a family, etc.); and 3) they felt that sexual activity could not exclude the possibility for procreation (with a few exceptions like the infertile).
In addition to accepting that attraction to the opposite sex was fine, other fathers (Chrysostom, Gregory of Nyssa, etc.) accepted that pleasure was also a natural human characteristics, and thus saw no problem if it was experienced within the proper context. The proper context, however, was narrowly defined: male/female sex, with the male in the dominant position, and the fronts of the couple facing each other. I've gotten flamed for saying that before. Sorry, you may not like it, but just because you don't find something that particular in a Homily by Chrysostom, that was the way things were, and you will find it in the penitential literature of both the east and west up through the 20th century. That doesn't mean that all Christians went by that teaching, of course, but that was the teaching nonetheless.
Maturbation would have been one of the least acceptable expressions of sexuality, because: 1) there would be no chance for procreation, 2) it indulged (rather than avoided) fornication, and 3) it usually indulges lustful thoughts. Not a few other people equated it with abortion, and considered it the "destruction of a soul," giving penances that could last for years. Obviously mutual masturbation was also not allowed, for some of the above reasons. From what I've read, young people were generally let off easy for the first few times, though if it was a habit, or you were married, the penances could get pretty difficult/lengthy.
For the most broad overview of sexuality in the early Church, the best book would probably be John T. Noonan's Contraception: A History of Its Treatment by the Catholic Theologians and Canonists
. The book does have some flaws, but just about anyone who writes about sexuality in the early Church quotes this book. Noonan's book includes some early canonical/penitential information, though that is mostly from the west. A better book for this information would be Sex and Society In the World of the Orthodox Slavs, 900-1700
by Eve Levin. There are some issues with this book as well, but it is one of the most researched books that I've read, and gives a good idea of what the general feelings of the Slavic Orthodox Churches were for everything from homosexuality to masturbation to playing footsies (yes, believe it or not, in at least one area there was a penance given if a single person confessed playing footsies in a flirtatious way).
From a more traditional Orthodox/Catholic perspective, the only one I'd recommend is the book Women and Men in the Early Church: The Full Views of St. John Chrysostom
by David Ford. Sometimes I think he has rose-colored glasses on, and the book comes off more like an apologetic than a scholarly work (and in fact a good portion of the book is spent dealing with various criticisms of the fathers by feminists and such), but he still does the best job that I've seen in presenting the Orthodox view of sexuality.