Sounds like a good trip. If you have any questions you can PM me. I agree with the other comments that it could get a bit still and hot in Hadley. In those conditions, the outer harbor might be better. We have anchored there in the past. Some boat wake from Woods Hole gets in. As to the moorings, I drove around in my dinghy and looked at a few of them. Mine had a new pendant above with a 5/8" Yale mooring line (a little light for a boat my size) with 1/2" chain below. Pendant still had the label so had been replaced recently. So apparently someone is maintaining them. Other pendants i looked at were older, but heavier and looked to be in good shape. No idea what is on the bottom. None of the pendants had chafe protection at the boat end so one might find one sawed through by prior misuse. Would be good if any TF ers have experience with any of these moorings failing in a blow.
The moorings at Cuttyhunk have a PVC upright 4' shaft that presents the end of the pendant, which is protected by a metal thimble. When you grab it, you can lift it higher with some effort when attaching, but only a few feet. Mine was new and looked like 7/8" or so. I saw some folks had wrapped a rag around the thimble as, in some conditions, the end of the upright shaft can bang against the hull.
Unlike Hadley, Cuttyhunk can get pretty rough if the wind moves N so I would be looking for something more substantial here than in Hadley. I didn't inspect any other moorings in the other fields. We do not fit inside. If you stay on either outside mooring field, you might want to select one or the other based on wind and wave protection.