Hi, I want my bitcoin core node to be reachable by Tor to other peers to contribute to the network. Do I need to add an onion address under Bitcoin Core > Interfaces > Peer P2P > Add Onion Service?
Yes, if you want peers to be able to reach your Bitcoin Core Node via tor, that is the way to go.
You can also take this further and set up a public IP via StartTunnel which will not rely on the slow and unreliable tor connection and will still keep your home IP private.