It seems a lot of hassle just to use a lounge tbh, plus don't forget the $4 fee to get back to the International terminal. Why not just head to a hotel ?

You don't say whether your lounge access is via OW status or by travelling business/1st class. If the latter then also consider that if your flight to Newcastle is on a separate ticket to your international flight you will not have automatic lounge access rights so may be denied access anyway

Dave