Bill has over 30,000 slides he needs to digitize. Leo says that 30,000 slides are untenable to digitize. So Leo recommends triaging and culling that number to a more manageable collection of those he absolutely must archive. Then go to a company like ScanCafe.com. They will not only digitize them, but they will clean them and then save them to a DVD or thumb drive for him to have. He also wants to tag the photos with metadata like when, where, and who. Leo says Camera Bits PhotoMechanic is great for that. It's around $140 and comes with a 30-day free trial.
Bill is also having issues with Google Photos saving 4K images at full quality. Leo says that while he has unlimited high-resolution storage with Google Photos, those aren't exactly full resolution. He has limited space for that and Google may not even support 4K images. So look around for an alternative. If he's an amazon prime member... free unlimited storage.