As I understand it, DHT was created to eliminate the need for websites to host the .torrent metadata files and hence trackers were to be deprecated.

If I create a new torrent, and am well connected via DHT nodes (600+), once I am seeding the new torrent, will it be discoverable by others somehow over DHT?

I understand I can provide a magnet link, and can also upload my .torrent file to a tracker site, but if I don't do either, is there any mechanism for others to discover and download from me?

DHT and magnet links are often used together but getting peers' addresses and getting torrent metadata is separate. DHT acts like a decentralized tracker - you can learn IP addresses of peers sharing a torrent, usually DHT is a backup for a tracker. Magnet links (Extension for Peers to Send Metadata Files) allow to "join a swarm and complete a download without the need of downloading a .torrent file first" by downloading metadata from connected peers directly. Usually magnet links contain a tracker URL, so it isn't necessary to have DHT enabled in order to start downloading from a magnet link - program will get peers from the tracker.

In order to download a torrent you have to know it's info hash value, that means you need a .torrent file or magnet link. Usually you get these from an indexing site, where someone uploaded the .torrent file earlier. There is a site that automatically indexes torrents found through DHT only, search for "BTDigg" or "DHT search engine".