Great post! My only fine tuning on what is posted so far is this:
There is friendship, then; the greatest pleasure, and surest path to happiness
I think the second clause is almost exactly correct, but I would say that what Epicurus saying is that the whole the pleasure of having a friend is great, and such relationships are actually or at least virtually essential, I do not think that there is an absolute ranking of pleasures that would allow us to call friendship "the greatest pleasure."
A fine point I easily grant, but given our focus on explaining the nature of pleasure as accurately as possible. I think an important one.
Am I forgetting any passage that would justify exactly calling friendship "the greatest pleasure"?
We definitely need to expand the thread and be sure we touch on the explanation for the opening of Lucretius Book Two.
And I think we will also find more apt material on friendship in the Torquatus material in Book One of On Ends that we will tackle next week (section 65 et seq. If I recall correctly)
And yes there is much in Diogenes of Oinoanda to incorporate, in addition to "circumstantial evidence" and "logical implications" that may not be explicit