I have read somewhere that CB Query can take and display any information in the MySQL table and display it as a CB field right?
Yes.
And we can hide this field from profile?
Sure, its display behaves like any other field.
CB Auto Action can then act on any of the Query fields no?
Yes, you can substitute in the query field value like any other field.
If my assummptions above are correct, we can use AA and Query field for literally building any plugin for any component (as long as the action is happening within CB).
I guess so. It really depends on what you're trying to do I suppose.