Don’t buy books/video/music on physical media unless it’s hard/impossible to get a digital version. But also don’t rely on IP subscription services either. The Cloud is great as part of a backup strategy: but not as an exclusive service that could gate your access to your content.

Digital storage is great because it can hold anything: books, shows, games, whatever. And it can be easily copied, and sent around the world. Have some space you own: redundant and automatically backed-up to a Cloud service… then enjoy it for years. It will feed your ebook readers and media players and homelab devices for a long time, and take up almost no space.

One big one. You can buy a second big one later :)

It will work as you describe with no issues: vibration won’t be a problem. Use large/slow case fans (and even for the CPU consider a 92mm model if 120mm won’t fit) and it should serve you well for years. Good luck!