I generally agree and have landed at "if there's something outside our known universe, then we can't know anything about it." There may be objections to this, but if all we have to go on is our observations of causality, physical laws, time, etc... it seems difficult to project assertions on what might very well lay outside of those observationally-derived rules.

In any case, the theist doesn't start with what we observe, the argument always starts with defining god as a necessary being that by definition (redundant) doesn't require a cause. Thus the answer to "what was the first cause?" handily has an answer waiting for it... by definition.