(Continuing) Thirdly, you assume that causality is applicable to everything, while it may not hold true for the universe itself. Even if you accept a First Cause, the universe could be its own first cause. You are just pushing the problem back a step.

If you believe in abiogenesis and the evolution of man, then life can come from non-life and intelligence from non-intelligence. You did not prove that these were impossible, so the First Cause need not be sentient. Also, you are confusing "universe" and "existence" The universe we see today had a definite beginning (Big Bang) but that does not mean that all of existence began then, only that we are limited to knowledge about our universe.