You can run multiple frontends and backends on multiple machines. And I’m pretty sure that you can also run PostgreSQL on multiple machines.

Slightly related: German hip hop song about a piece of wood.

I would honestly drop the “link aggregator” part completely and just call it “discussion forum” or “discussion platform”. “Link aggregator” sounds pretty technical and like it just collects links which seems almost pointless. And the links aren’t even mandatory when creating a post.