God's God

[Neo-Scholastic]

...And god's creator is beyond even that, then, right? Why would "If god did not have a beginning then you have an infinite regress of causes and effects, one that is incapable of causing itself." be invalid?

You do not understand that there are different kinds of cause. An uncaused cause does not lie within the temporal causal chain.

It should be noted that there is not necessarily a reason to think existence itself needs a cause.

Correct. Reality exists, except you have limited your thinking to physical reality. Physical reality needs a cause because it has finite attributes that have beginnings. The cause of the physical universe is the timeless, changeless, spaceless, and immaterial something on which time, space, change, and material depend.

The only know instances (as far as I know) of the existence of physical matter beginning would be quantum fluctuation, which is not caused.

Do you have a deep understanding of quantum mechanics? I don't. That is why I look to the metaphysical principles that allow us to posit various models of physical reality.