what is the "word" of God really?

You are correct! No words are equal to the bible!

We are warned Deuteronomy 4:2 “You shall not add to the word which I command you, nor take anything from it”(also Deuteronomy 12:32).

I see the problem here.  You have interpreted this scripture in such a way that "the word" means "the bible" even though when these words were written the new testament was yet many centuries off!  By your own interpretation of Deut 4:2, the entire new testament and much of the old testament is apostacy because it "added to the word of God" as warned against in Deut 4:2!  Do you not see the problem here?  this is why Spirit led interpretation is so essential. 

God's word which does include the entire inch thick bible, old testament and new is every word He has ever spoken to the hearts, minds and spirits of His millions of servants throughout all of human history... and the bible is only one inch of this.   It's really quite alarming how blinding the doctrines of man as inspired and sponsored by satan's kingdom can be.   Please don't fall for the wildly popular (narrow is the path) but fantastically lying doctrine of man that all of God's "words" spoken to millions of His servants throughout all history and including today are not part of His "word".  Believing and living these false doctrines of man amounts to nothing less than bible idolotry / bible worship.  The living God of all creation can not be condensed to an inch and will not be quenched and put into a tiny box!  Remember also that the bible is not the fourth member of the trinity and only because lying man with his false interpretations said it's the only word of God is it believed by the blind led by the blind followers of man to be this.  He who has ears to hear let him hear and may the scales fall from all the blind eyes.  "Lord we pray you obliterate all the many lies of man that many have come to embrace and that you fill us only with your truth".  God bless you thorns in Jesus name.  I have high hopes for you.