What can we know about anything and everything?

I don't know.

That's not possible. Remember, there has to be limitations.

We can not possibly know everything even though there is isn't anything we can't not possibly learn.  There is what is called a "Matrix argument" :  We are but ants in a petri dish that "God" created.  That is how he existed before the universe (so they say) because supposedly there is another universe outside of the universe.  (so they say). 

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The concept of "The Collective Unconscious" as proposed by Jung brings us to a conclusion that you should have considered: it is impossible for the finite mortal mind to understand everything.  However, limited as we are we can access a vast body of insight by means of trained spiritual awareness.

That means we must divorce ourself from atheist demands for exhaustive proof, as the proof these people sought would be beyond their comprehension.  Even if they found it, that proof would disprove every thought an atheist holds dear.  That limits atheists to utter nonfunction.

To grow intellectually we must first grow spiritually.  That is the cosmic law.