The following resources are a helpful start in Early Church studies.
Societies
International Association of Patristic Studies
http://www.aiep-iaps.org
International Conference on Patristic Studies, Oxford
http://www.oxfordpatristics.com
Study Resources
Biblindex
https://biblindex.hypotheses.org/
Center for Early African Christianity
http://earlyafricanchristianity.com
https://www.earlyafricanchristianity.com/resources
Fourth-Century Christianity
http://www.oxfordpatristics.com
Institut des Sources Chrétiennes
http://www.sourceschretiennes.mom.fr
PLGO
http://plgo.org/?page_id=2150
Revue d'Etudes Augustiniennes et Patristiques (1955–2005)
https://www.brepolsonline.net/loi/rea?expanded=15