Question: "To be Orthodox, must a person hold to the distinction in God between essence and energies?"
Let me first ask a slightly different question: to be Orthodox, must a person understand the distinction between God's essence and energies? The answer to that question is "no". Salvation is not a pop-quiz in theology. There are many Orthodox faithful who are not capable of understanding theology on an intellectual level (very young children, those with mental handicaps, etc.). But an Orthodox Christian certainly must not reject this distinction. This distinction was an important part of St. Gregory Palamas' defense of hesychasm, and his defense of hesychasm is celebrated as a second triumph of Orthodoxy on the second Sunday of Lent... and so the Church has clearly embraced St. Gregory's understanding of this question. Orthodox Christians are not free to have their own opinions on matters that the Church has a clear and universal teaching on. And certainly, every Orthodox Christian should try to understand as much of the teachings and Traditions of the Church as they possibly can.
For more on what the Church teaches on this question, see:
Vladimir Lossky on the Essence and Energies of God
Theosis and Orthodoxy
GOD: Essence and Energies (from the Illumined Heart Podcast) (It is a good idea to take the suggestion at the beginning of this podcast, and listen to this several times).