An argument for Eternalism Seems right, and the success of relativity might bolster the argument. But I don’t think you sufficiently defined “base reality”. Is it just a classification of everything taken together? Can base reality be experienced phenomenalogically (by us or god?) or is it just a way of explaining things?
Also, must infinities necessarily be avoided? Spinoza took the existence of infinity as one of his fundamental assumptions. My own point of view on this is that infinities do exist, but by definition cannot be grasped all at once and therefore time MUST exist.