Pretty much all of the real functionality is there. I ended up using polka for the server rather than express because that's what sapper uses so I figured I'd get to know it. It turns out it's exactly the same as express, just a tiny bit faster.
This app uses sapper's prerendering functionality, which I've been wanting to try out, so this was good.
Next I should probably nail down the interface then add in the niceties like the duplicates warning and such.