Unsplash is another perfect example of doing nice stuff with Service Worker. Someone should do it. Then you would only need a Chrome Extension that randomizes between URLs for the new tab.
Again, you don't need a Chrome extension to randomize between URLs. Just write a simple HTML+Javascript page that redirects to a random URL from a list, and set it as your start page.
Exactly, but I use Noosfeer. It's the same thing but for movie screenshots and there's extra info like IMDb, trailer, etc at the bottom.