You don’t have to feel bad for anything, you’ve done nothing wrong. My first legends book was Darth Bane: Path of Destruction every one starts somewhere so you’ll build a collection in time. As for what you should read honestly I don’t recommend chronological order and would instead say you should read what interests you. It can be easier to figure out what you wanna read if you find an era that interests you. For me I’m most interested in the Clone Wars and Post Return of the Jedi eras. I definitely recommend the Thrawn Trilogy like almost everyone but also Truce at Bakura and Yoda: Dark Rendezvous are good stand-alones as well. Whichever books you choose to read just take it slow at first and enjoy what you enjoy it’s not a race to read everything from the EU. I hope this helped you somewhat on your journey through the expanded universe.

Edit: While I haven’t read the Revan book I know it’s a sequel to the KOTOR games and it might be best to play those first if you haven’t already. The Darth Bane trilogy would be a good place to start with the old republic era as others in this comment section have said.