First order logic, set theory and God

[I_am_not_mafia]

P1. The principle of sufficient reason: All phenomena are either self-caused (i.e. A->A) or other-caused (B->A; B is not equal to A) but not both. Put another way, this principle says that the question "why?" is always meaningful. Everything happens for a reason.

This sounds like a 'first cause' premise. There are a variety of hypotheses for the initiation of our universe for which the math and physics work. I don't see how this premise would invalidate any of them.

For example what if there is no first cause?

Theists argue that their god needs to be the first cause, but what caused their god to exist? And if it didn't need a cause to exist, then why does energy need a cause to exist? After all, science already tells us that energy cannot be created nor destroyed. Why do we need to add an undefinable god into the mix?