While we still don't have a release date for the Steam version of Wildstar, the portal page has been published. Of particular interest is a developer FAQ that is now live on the community hub. You can find out how to make an account, whether or not you will have to re-download the client (yes) and whether or not Steam and desktop can adventure together (yes).
Q: So, how will you be able to link your steam account to your existing NC account, what will the process be exactly? And once you do link it, will you have to login to your NC account or will you not have to login at all?
A: The first time you run the game from Steam, it will prompt you to log into the game just as you have before. Doing this will link that account to your Steam account. Every subsequent time you run the game, it will automatically launch and you won't be prompted to enter your account details again. But be aware, if you have multiple accounts be sure which one you want linked, as only one of them can be. If you accidentally link the wrong account, you can put in a ticket with support to have it reset.
You can read the full FAQ on the WildStar Steam portal.
Thanks BlueTurtle13 for the tip.