The Elder Scrolls Online

I’m thinking about a return to ESO after a very long time away. This is a stupid question that’s probably already been asked and answered somewhere upthread, but…

…how do ESO and it’s expansions work on Steam? I own Tamriel Unlimited on Steam, and at some point I bought Morrowwind on the cheap as well, so it looks like I own what is now referred to as the “Standard Edition” on Steam. I see that I can purchase the Elsweyr Upgrade and add that content, but it appears that Summerset is no longer an option to purchase separately, and neither is the “Gold” version content, with the smaller DLCs. Are these now only available via the in-game Crown Store to unlock on my ESO account?

When I played, I played a box copy of Tamriel Unlimited and logged directly into the ESO servers. The Steam copies of the base game and Morrrowind that I own I actually purchased after I’d quit playing. I assume that after I launch the Steam version of the game, it will take me to the ESO servers, where I can use my old ESO account to simply login like I used to, and that my old characters may still be there?