Hi kmklint, I went on a few guided hikes in the area with Amangiri guide, I think they said they've been in this area for 20 years, so they're really knowledgeable. The resort offers a "testing hike" for guests per day, free of charge, they do charge you for more challenging hikes or the ones off property.
I also took a boat out on lake powell one day, but it was still pretty cold, it's my first time to lake powell and the view was absolutely gorgeous, I can see why this is such a popular summer destination!
I actually spent more time on the deck during the day than at night! I like standing on the deck and just overlook the whole mesa view, star gazing is great but the place is just so quiet at night it could be a bit creepy! There's no light pollution at all but I did not see as many stars as I expected though, I'm not sure if it's because of the season? I was there during full moon so I enjoyed moon-gazing more than star gazing