In terms of daily practice and general beliefs, what would one expect from an Ethiopian Jew prior to Ezana's conversion of his empire to Christianity? How would he observe the Sabbath, for example?
More broadly, are there any really good books about religion and culture in Ethiopia in that era? What should I be reading if I want to get a sense of that time and place?
I'm an archaeologist, not a historian, and from an archaeological perspective, we don't really know anything about daily life and ritual among Jewish people in Aksumite Ethiopia. Even early Christianity in Ethiopia is a bit muddled as a lot of textual evidence from the period is rather formulaic inscriptions rather than detailed historical prose. However, I can give you some suggestions for things you might like to read that would give you a better impression of what Ethiopia would have been like for the people living there and the evolution of Christian thought and life through the post-Aksumite period.
Sergew Hable Sellassie's (1972) "Ancient and Medieval Ethiopian History to 1270" is a good, detailed introduction to Aksumite Ethiopian history, though at this point, it's a little dated since the archaeology and theory has advanced quite a bit since then. Nonetheless, it still covers all the major historical work and inscriptions that we still base a lot of research on. It's also a good foil to Tadesse Tamrat's (1972) "Church and State in Ethiopia, 1270 - 1527." Together, they're the essentials first reads for most Ethiopian scholarship. I'd also throw in J Spencer Trimmingham's (1952) "Islam in Ethiopia" for a perspective on Ethiopian history from a more Muslim/Arabian-oriented perspective. Again, it's a bit dated, but still covers a lot of important first-hand material; they've all been recently republished by Shama Books or Red Sea Press too, I believe. Harold Marcus' "A History of Ethiopia" (2002) is also really readable if you're looking for something slightly less academic (though I think all three of the above are very well-written and easy reads), but I'd say he doesn't delve as deep into the older history as he could.
For more religious history in Ethiopia, I would also check out the following. However, I have to say, we have a lot more detail on religion and religious practice in the Post-Aksumite period, and as that is also my focus, I know more of the relevant lit there. You may want to start following the work of Michael Harrower at Johns Hopkins. He's unwittingly discovered the remains of the earliest church so far under excavation in Ethiopia and is sure to publish some fascinating (though perhaps very academic) stuff in the coming years. *Note, rather than re-write all these citations by hand, I'm going to copy and paste them from my master bibliography, but they're formatted so they'll look a little ugly; apologies. If you can read French, let me know and I can add some more.
Vyhmeister, Werner K.
1982 The Sabbath in Egypt and Ethiopia. In The Sabbath in Scripture and History. Kenneth A. Strand, ed. Pp. 169-189. Washington: Review and Herald Publishing Association.
Abir, Mordechai
1980 Ethiopia and the Red Sea: The Rise and Decline of the Solomonic Dynasty and
Muslim-European Rivalry in the Region. London: Frank Cass and Company, Ltd.
Bartnicki, Andrzej and Joanna Mantel-Nieko
1969-70 The Role and Significance of the religious conflicts and people’s movements in the political life of Ethiopia in the seventeenth and eighteenth centuries. Rassegna di studi Etiopia. 24: 5-39.
Beckingham, C.F. and G.W.B. Huntingford, eds.
1961 The Prester John of the Indies: A True Relation of the Lands of the Prester John.
vol. I and II. Francisco Alvares, auth. Lord Stanley of Alderly, trans. Cambridge:
Cambridge University Press.
Bekele, Shiferaw
2001 The Shadowy Bishops of the Ethiopian Church in the First Millennium of its
History (4th to 14th centuries): A review article. Journal of Ethiopian Studies. 34(1): 103-112.
Budge, E. A. Wallis, trans.
1922 The Queen of Sheba and Her Only Son Menyelek, Being the History of the
Departure of the Covenant from Jerusalem to Ethiopia and the Establishment of the
Religion of the Hebrews and the Solomonic Line of Kings in that Country. A
Complete Translation of the Kebra Nagast with Introduction by Sir E. A. Wallis
Budge. London: Medici Society.
Crummey, Donald
2000 Land and Society in the Christian Kingdom of Ethiopia. Chicago: University of
Illinois Press.
Finneran, Niall
2002 The Archaeology of Christianity in Africa. Stroud: Tempus.
2003 The Monasteries of Shire, Northern Ethiopia. Ecclesiology Today. 30: 3-10.
2007 Ethiopian Christian Material Culture: The International Context. Aksum, the
Mediterranean and the Syriac World in the Fifth and Seventh Centuries. In Incipient
Globalization? Long-Distance Contacts in the 6th Century. Anthea Harris, ed. BAR
International Series, 1644. Oxford: Archaeopress.
Finneran, Niall and Tania Tribe
2004 Towards an Archaeology of Ethiopian Monasticism: Contexts and Themes. In
Belief in the Past: The Proceedings of the 2002 Manchester Conference on
Archaeology and Religion. Timothy Insoll, ed. Pp. 63-73. Oxford: Archaeopress.
Heldman, Marilyn
1992 Architectural Symbolism, Sacred Geography and the Ethiopian Church. Journal
of Religion in Africa. 22(3): 222- 241
Kaplan, Steven
1984 The Monastic Holy Man and the Christianization of Early Solomonic Ethiopia.
Studien zur Kulturkunde, 73. Stuttgart: Franz Steiner Verlag Wiesbaden.
1986 Court and Periphery in Ethiopian Christianity. Asian and African Studies. 20:
141-152.
Kirwan, L. P.
1972 The Christian Topography and the Kingdom of Axum. The Geographical
Journal. 138(2): 166-177. London: The Royal Geographical Society.
Levine, Donald N.
1965 Wax and Gold: Tradition and Innovation in Ethiopian Culture. Chicago: Chicago
University Press.
Pankhurst, Richard
1966 State and Land in Ethiopian History. Addis Ababa: Institute of Ethiopian Studies.
1967 The Ethiopian Royal Chronicles. R. Pankhurst, ed. Addis Ababa: Oxford
University Press.
Schmidt, Peter and Matthew Curtis
2001 Urban Precursors in the Horn: Early 1st Millenium BC Communities in Eritrea.
Antiquity. 75: 849-859.
Tamrat, Tadesse
1970 The Abbots of Dabra Hayq, 1248-1535. Journal of Ethiopian Studies. 8(1): 87-