A facebook employee explained me how tracking works. Its not the email address Meta is concerned about. Its the IP, device identifiers and location. Meta doesnt care about the email at all apart from sending you emails for notification. Even with a fake email they exactly know who you are. Let's say you visit CNN.com which has facebook tracker. Facebook has the IP and the device identifiers. Now you login with fake email account on Instagram, facebook knows that's the IP ans the same device hence it "must" be the same person That's how facebook creates shadow profiles.
A tor node or relay is just someone running and configuring tor on their server to accept and forward connections to the tor network being part of the chain. Normally a chain has three nodes: an entry , a middle and an exit.
Onion repos are software repositories in this case for the Debian Linux operating system that contain firmware and package updates and are hosted as onion services accessible over tor.