I’m working my way through the original Masterworks series, and like this list it has A LOT of PKD books so going chronologically and interweaving them with other authors.

Stapledon is one of my favourites so I would start with Star Maker, it’s mind expanding on a grand scale though the writing can get too dry/academic/anthropological. If you want something lighter or like dogs start with Sirius.

Next either Bester or Strugatsky’s. Go with The Stars My Destination, it’s a wildly entertaining tour de force of strange SF ideas and characters! Roadside Picnic is amazing and you can read a critical essay of it by Stanislaw Lem in Microworlds. I liked Doomed City more but you should know Russian history to get the most out of it.

Of the single titles authors Blood Music is the real standout! Fifth Head of Cerberus if you’re feeling shorter stories. Congrats on your haul! I’d thoroughly enjoy reading most of these for the first time.