Start with high-confidence orthodox christianity books, then narrow by subgenre or adjacent topics.
The Way of a Pilgrim
Nina A Toumanova, Anonymous
On Difficulties in the Church Fathers: the Ambigua
Maximos the Confessor, Nicholas Constas
Introducing Eastern Orthodox Theology
Andrew Louth
Now Is the Accepted Time
Theophan the Recluse
Ethiopian Christianity
Philip F. Esler
