Firstly the thread title seems oddly incongruous with a debate forum? One wonders why you’d come here of all places to post such a question. I can’t speak for anyone else but debate can be very edifying.
Not as an immutable fact no, but one can establish a weight of objective evidence that supports a fact as irrefutable.
Scientific laws are statements, based on repeated experiments or observations, that describe or predict a range of natural phenomena A scientific law is a statement that describes an observable occurrence in nature that appears to always be true.
Right and wrong are subjective evaluations, and while morality is subjective, objective and irrefutable facts do exist, as not everything is entirely subjective, it is an objective fact that the earth is not flat, or that all living things evolved slowly over time, for example, these are irrefutable and objective facts.
That’s a subjective claim.
Atheism doesn’t have a first principle, it is the lack or absence of belief, beliefs are the affirmation of a claim, and so carry a burden of proof, a lack of belief does not, as it need not involve any claim.
Luckily it is not mandatory. However I don’t see a critical examination of claims or beliefs as ever being pointless. Either for those who hold them or for those who do not, NB It’s noteworthy that you are not defining any deity here, and some concepts of deity are eminently falsifiable, where the concept is unfalsifiable I must of course remain agnostic about them, but I must also withhold belief, as this is the only rational unbiased position, thus I am both an agnostic (where nothing is known or an be known about a belief) and an atheist as I don’t believe any deity or deities exist outside of the human imagination.
Omnipotent is defined as possessing limitless power, I think you mean omniscient, and again one need not know that a claim is false in order to withhold belief, indeed to suggest any claim gains credence because of a lack of contrary evidence is an argumentum ad ignorantiam fallacy.