Marta,
There are graduate level courses on science and religion or science and Christianity with a library of books to consult. The ex-nihilo theology would be one of many topics. Theology has two main focuses. One being doctrines. The other being philosophy. However, theology is always religious philosophy, and like philosophy, theology is based upon the study of the fundamental nature of knowledge, reality, and existence but limited to religious ideas concerning these things. Are these, the things divine revelation addresses?
Ex-nihilo is related to the first cause. The first cause may be explained as a natural event or a transcendent event. Because neither of these first causes is currently testable, both are metaphysical speculations in the study of philosophy.
Modern educated Americans (and others) attempt to understand reality using reason. Approaching divine revelation from such a modern perspective generates rational philosophical questions and speculative explanations that in the history of the Church has been the domain of Christian scholars rather than the lay faithful. Considering the above parameters limiting how theology ought to be surveyed, those who seek to grow in their divine relationship might do well by avoiding inquiries about science and philosophy in matters of the Christian faith. In my opinion, divine revelation as recorded in the Bible does not intend to address science or answer metaphysical questions other that what has been clearly revealed. On the other hand, it seems imperative to know what has been revealed.
The launch for properly understanding biblical divine revelation begins with character and nature of deity, that is, the LORD is revealing specific things about who He is. Concerning creation, the divine purpose of the creation is to glorify the LORD by demonstrating his character through the plan of redemption. There is only one plan, no plan B. However, theologians attempt to rationalize the revelation, the LORD created to redeem through Christ a humankind who is incapable of deserving divine redemption. His plan reveals to the creation what deity intends humankind to understand about deity. The only answers revealed through revelation are to address this plan. The question about ex-nihilo is not relevant theologically, doctrinally, or biblically.
The referenced biblical texts clearly reveal the LORD as Creator, but are not definitive concerning if creation was out of nothing or out of pre-existing matter. The faithful Christian ought to read Job 38:1-42:6 and humbly accept God has revealed in part; that is, a divine revelation governed by the divine plan to glorify deity rather than to describe a systematic theology or to provide answers generated by rational philosophical questioning and speculative explanations.
“But without faith it is impossible to please him: for he that cometh to God must believe that he is, and that he is a rewarder of them that diligently seek him” (Hebrews 11:6 KJV). With regards to thinking as modern educated Americans, Christian discipleship requires following the resurrected Lord Jesus rather than theological comprehension.
References: Genesis 1:1ff, Job 38:1-42:6, Psalms 33:6, Psalms 148:5, John 1:3, Colossians 1:16, Hebrews 11:3