Thomas Aquinas conceived of the transcendent nature of the Christian God in the thirteenth century, labelling God as timeless, omnipotent and omniscient. What was the general consensus on God's abilities/forms prior to this?

These attributes of God were very well established and agreed-upon in Christian theology long before Aquinas' time. Aquinas was not setting out to do anything new; he was a systematizer, not an innovator. I would say that by the 4th century, there had already been extensive discussion of these, especially in relation to the Arian and Nestorian controversies, and from the influence of Neo-Platonic philosophy on the development of theological formulations.

To use one example, Augustine of Hippo in the late 4th/early 5th century talked extensively about the omnipotence and omniscience of God, especially in relation to questions of free will vs. fate. From the City of God:

We do not deny, of course, an order of causes in which the will of God is all-powerful. On the other hand, we do not give this order the name fate, expect in a sense in which the word 'fate' is derived from fari, to speak. For, of course, we cannot reject what is written in Holy Scripture: 'God hath spoken once, these two things have I heard, that power belongeth to God and mercy to Thee, O Lord, for Thou wilt render to everyone according to his works.' The 'once' here means 'once and for all.' God spoke once and for all because He knows unalterably all that is to be, all that He is to do.

Part 1, Book 5, chapter 9, emphasis added. It's hard to pull a single quote out of Augustine's broad treatment, but that one shows reference to both omnipotence and omniscience.

Cyril of Jerusalem also spoke of the omnipotence of God in his catechetical lectures, with the 8th lecture devoted to the topic of God as Almighty. This topic came up in reference to the Nicene Creed, in which Christians confess "I believe in God, the Father Almighty, Maker of heaven and earth." Dating from the Council of Nicaea in 325, we see the omnipotence of God clearly included there.

All these attributes of God are also, I should point out, not purely products of philosophy, but the Church Fathers found support for them in the Biblical texts as well. 1 John 3:20 says that God "knows all things," Jeremiah 23:24 that God is omnipresent, and so forth.