I sometimes feel that the reputation system in WoW has gotten out of hand. I'm glad that new players will just have the races available to them

If you stopped in WotLK I want to say start at Cataclysm and play through Legion, but that is a serious time investment. I think you'd be OK just playing through Legion, though there are some things it draws from prior expansions as well. Specifically the return of Gul'dan in WoD.

If you've hit level 60 I don't believe you can use Chromie time. Since you mentioned you've played through BfA I'm going to assume you're in your 50s, so I would just say use Wowhead to locate the intro quests for Cataclysm and start there. I hope that's not too much of a cap-out answer.