Larry Hurtado has a very good blog post on The Cinderella Century in Early Christianity, where notes the incredibly significance of the second century for the emergence of later Christianity.
I concur with his assessment. In fact, I now deliberately prod potential Ph.D students to consider working in the second century rather than in the first century, because (a) I am sick of reading Ph.D proposals about Paul’s use of Isaiah in Romans; and (b) The second century is where New Testament and Church History beautifully merge together and there is much work to be done here. Two Presbyterian scholars, Charles Hill and Michael Kruger, have done some excellent stuff in this field,investigating textual, canonical, and historical matters in relation to the emergence of the proto-orthodox church in the second century. I recommend them as a model for others to follow in bridging NT studies with patristics.
At the moment I am working on a project called The Gospels of the Lord: How the Early Church Wrote the Story of Jesus, where a significant amount of my research, reading, and writing pertains to second century authors from Papias to Clement of Alexandria. There is so much work here to do, the fields are ripe for harvest, consider a research degree in this area!
Some works I’d recommend are:
Charles Hill & Michael Kruger (eds.), The Early Text of the New Testament
Charles Hill, Who Chose the Gospels?
Lee Martin McDonald, Forgotten Scriptures
Sebastian Moll, The Arch-Heretic Marcion
Michael Bird & Joseph Dodson (eds.), Paul and the Second Century
Antti Marjanen & Petri Luomanen (eds.), A Companion to second-Century Christian ‘Heretics’
Larry Huratdo, Early Christian Artefacts
Paul Foster (ed.), Early Christian Thinkers