I must admit I've been a bit pokey about getting my social proof for this paper. However, I recently heard back from Professor Kerr and his suggestions and thoughts were immensely helpful. I'd expressed my difficulties in finding secondary sources for my topic, as asked for his view on Christ's character in Paradise Regained. He responded:
For a thoughtful take on desire with respect to Paradise Regained, look at the Milton chapter in Ryan Netzley's Reading, Desire, and the Eucharist in Early Modern Religious Poetry. It's fairly theoretical, but quite good--and at minimum it should point you to other useful sources.
As regards the Son in PR, I tend to think of him as the site of a complex meditation on the conditions of human freedom. Depth of character is not an analytic category to which I've given much thought with regard to this poem (which is not to say that doing so would be unworthwhile for you).
The book he mentioned isn't available at the library, but I found some excerpts on Google Books that were pertinent to my subject. Netzley writes, "In Milton's paradisal sinless Eucharist, the emphasis falls on desire, but not an achieved redemption or one forever repeatable ritual." I think this means that Milton intended the sacrament, and by extension other aspects of spirituality in the book, to be an act that could sate spiritual hunger. In addition, the phrase "achieved redemption" made me stop and think.
I've been assuming that the characters I'm writing about all want redemption in their own way, and while I don't entirely agree with Netzley's assertion on this point I do see how the term is a little broad. Satan doesn't want redemption, he wants a kind of revenge. Christ has no need for it, and while Samson is placed in the text as a redemptive character he really yearns for forgiveness. I'm quite obviously still working it through, but Netzley's text has given me a few ideas for where to take my paper in its conclusion, as well as providing me with some excellent sources. So thank you Professor Kerr, I'd be lost without you.