Why does The Gospel Coalition’s Confessional Statement begin with God instead of Scripture or epistemology?
D. A. Carson (who drafted the statement) and Tim Keller explain in Gospel-Centered Ministry 
(The Gospel Coalition Booklets; Wheaton: Crossway, 2011), p. 6:
We also thought it was important to begin our confession with God rather than with Scripture. This is significant. The Enlightenment was overconfident about human rationality. Some strands of it assumed it was possible to build systems of thought on unassailable foundations that could be absolutely certain to unaided human reason. Despite their frequent vilification of the Enlightenment, many conservative evangelicals have nevertheless been shaped by it. This can be seen in how many evangelical statements of faith start with the Scripture, not with God. They proceed from Scripture to doctrine through rigorous exegesis in order to build (what they consider) an absolutely sure, guaranteed-true-to-Scripture theology.
The problem is that this is essentially a foundationalist approach to knowledge. It ignores the degree to which our cultural location affects our interpretation of the Bible, and it assumes a very rigid subject-object distinction. It ignores historical theology, philosophy, and cultural reflection. Starting with the Scripture leads readers to the overconfidence that their exegesis of biblical texts has produced a system of perfect doctrinal truth. This can create pride and rigidity because it may not sufficiently acknowledge the fallenness of human reason.
We believe it is best to start with God, to declare (with John Calvin, Institutes 1.1) that without knowledge of God we cannot know ourselves, our world, or anything else. If there is no God, we would have no reason to trust our reason.
This is an old debate as the Thirty-nine Articles began with God and the Westminster Confession of Faith began with Scripture.
While I have a slight preference for beginning with God, I am not impressed by the reasoning in the above statement. Starting with Scripture, rightly understood, is also a way of starting with God since it is His self-revelation. This only leads to foundationalism when we assume that we are the subjects and that God’s word is the object. When we remember that Scripture is the Sovereign God’s word to us this problem goes away. Correspondingly, we can easily run into problems by starting with God such as assuming that we can know what we are talking about apart from God’s self-revelation in His word.
The fact is that a confession of faith has to start somewhere. That starting point could reasonably be adjusted to address the problems that a particular culture is prone to fall into.
1. I would argue that any problem with the approach wouldn’t be that it’s foundationalist but with what is taken to be the foundation and how it moves from the foundation to other things.
2. How does replacing one thing in the foundation with another thing (in this case with God) going to make it no longer foundationalist?
I expect better of Carson and Keller. This is just uncareful use of philosophical terminology that they’d be much better off not using, but given that they’ve used it they’ve invited the criticism that they’ve used it improperly.