Any definition of God that's remotely connected to what people throughout history have meant by the concept must include (I believe) some characteristics that we would recognize as personhood, intelligence, purpose. Also atleast one of the following : superior power, superior wisdom, superior level of existence (to be superior to humans in atleast some way*).

"first cause" however is far, far, from being a universal characteristic of imagined Gods -- many ancient pantheons had their various Gods (even their supreme Gods) being born, growing up, occasionally overthrowing previous gods, etc.

So a minimalist concept of God wouldn't be limited to "first cause", and I don't think it should even include it as one of its elements.

If you want to describe a non-necessarily intelligent, non-necessarily purposeful "first cause", I would very strongly advise you not to use the word "God".