WHAT TO READ OF THE FATHERS?
I would say Jaroslav Pelikan’s first volume in his history of Christian doctrine, The Emergence of the Catholic Tradition, is an excellent place to start. JND Kelly on Early Christian Doctrine is another excellent starter. Other secondary sources that provide a good introduction include the works by Christopher Hall (Reading Scripture with the Church Fathers and Doing Theology with the Church Fathers) and Robert Wilken’s The Spirit of Early Thought. Gerald Bray’s Creeds, Councils and Christ is also very good. I also like Henry Chadwick’s two works on the early church: The Early Church (Penguin) and The Church in Ancient Society (OUP).
For primary sources, see Henry Bettenson, The Early Christian Fathers and his The Later Christian Fathers give good overviews. Augustine’s Confessions is a natural place to start. You may not agree with all you read, but it is a gem. Also the second-century The Letter to Diognetus is a gem—the cream of second-century Apologetics. I would also strongly recommend Basil’s On the Holy Spirit.