Some possible choices for background reading.
Thomas Cahill, How the Irish Saved Civilization: The Untold Story of Ireland's Heroic Role from the Fall of Rome to the Rise of Medieval Europe (Doubleday, 1995)
A very good read – gives you a good idea of early Christian Irish culture.
Edward C. Sellner, The Wisdom of the Celtic Saints (Bog Walk Press, 2006)
Its introduction (about forty pages) is the best way of getting aboard Celtic Christianity in a very short time.
Esther de Waal, The Celtic Way of Prayer: The Recovery of the Religious Imagination (Doubleday, 1997)
This book takes you into the spirituality of the Celtic centuries.
Daniel Taylor, In Search of Sacred Places: Looking for Wisdom on Celtic Holy Islands (Bog Walk Press, 2005)
A humorous and self-deprecating introduction to the way of pilgrimage.
Oliver Davies, ed., Celtic Spirituality (Paulist Press, 1995)
Compendium of the classic sources of early Celtic Christian spirituality.
David Adam, The Rhythm of Life: Celtic Daily Prayer (SPCK, 2007)
Prayer is what it is all about.
Comments by Herbert O’Driscoll, Marcus Losack, and John Leech. 2011 10/26
For St Andrew's, Tacoma, celtic fair 30 october 2011.