Afaik the data is stored on the server and if you logon with the same account you had on PC (steam is also pc btw
) you will be able to play the same chars again.
I geuss you need to install ESO on steam and just login then to the game like before, just started via Steam.
But this should be asked in the ESO forums (I bet there already are the same questions) and not here at the esoui (Addons) forum!