What Ourph says is true.
I can understand the impulse to want to know more about the original campaign, though. I went through that phase (and still am going through it to some extent). What must be resisted indeed is an obsession with somehow playing an absolutely "true" or "canon" version of the Castle. It's not going to happen. And in fact, trying to do so would indeed be counterproductive to the campaign. If you want to experience the "feel" of the original campaign, getting obsessed about "canon" Greyhawk would get you going in pretty much the polar opposite direction from where you want to go.
However. Getting to know details about the original castle, how some things came into play, what the general campaign was like, or some of its most iconic features and areas, may inspire you to come up with your own stuff and create from there. I know that's what it did, and still does for me, to this day.
So don't feel like you have to give up on your desire to know more about the original campaign. Just don't get obsessed about stuff like "canon" up to the point where your campaign would be some sort of reenactment of stuff that never was. Just let this stuff impact your imagination, and roll from there. You'll have a blast.