Both of those things are in fact implemented :). For seeding items, go to the "Add" page and there's a search bar (on desktop, it's in the sidebar; on mobile, you have to open the hamburger menu). I'll probably move the search bar to the main page to make it more discoverable.[1]
When you rate an item, are you sure all three items get replaced? If you rate one item, the ones below it should be moved up, and then the item on the bottom will be new. So if you rate the top item, you'll see a visual change in all items, but the other two items will still be there. Perhaps I should replace rated items in place without moving the others.