There are so many important Church theologians and writers between AD 500 and 1900 that you could never read them all in your life. I mean, seriously, there is no lack of documentation. There are countries and periods of history where we don’t know bupkis about the king or the battles, but we’ve got sermons galore and arguments about the nature of the Trinity.
The period of the Fathers is generally considered to end at AD 600. Everybody else is a “later writer”.
If you want to study the Fathers, you will probably want to get into one of the big series of translations. Most big university libraries will have something from the Catholic University of America series or one of the other ones. (There’s ones out of Oxford, out of Boston, out of St. Vladimir’s, and so on. Tons and tons of them.)
Beyond that, there are many large collections of “Collected Works” of theologians and also many translations of single works or smaller collections. If you read Latin, Migne’s massive collections of the Patrologia Latina and Patrologia Graeca are partially online and partially still going with new appendices of newly-discovered materials. They include pretty much every major theologian who wrote in Latin or Greek, practically up to his own day. There’s also tons of stuff in Syriac/Aramaic, Coptic (that’s Egyptian), Arabic, Gaelic, Frankish, and so on and so forth.
So there’s a lot of interesting stuff out there to read, some of which has English translations and some of which does not. The best thing to do is to read about Church history or saints, and then run a search on any writer who sounds interesting and authoritative. These days, that will probably give you a pretty good start on looking around for reading material.
