From the various guides online I thought I could level from 10-50 in whatever expansion I choose. I chose WOD and it was fine up to lvl 40, but then quests turned green and at lvl 45 - gray. I went back to stormwind, didn’t see any quests to begin BFA story or anything. Eventually took the portal to Boralus and started the war campaign.
Did I do something wrong? Do I still have to do the entire. war. campaign. again?
This is the problem, “whatever expansion you choose” doesn’t mean what you choose in your head, it’s what you choose on special interface for Timewaking Campaigns. You need to find Chromie in Stormwind, she is marked with Hourglass on map. When you talk to her UI shows up where you can choose one expansion and she will properly phase you, then it will scale up to 50.
They did it this way to preserve level order of expansions in case some one would like to solo them at higher level or something.