yes, you register fro the unit. mine is the older one, with the keyboard, but I am assuming that the one without a keyboard has some method of inputting data (probably using a scroll/cursor key to highlight an onscreen keyboard) as you will need to to set up wifi etc.
I do have a cover for mine - the Amazon leather cover with built in light. it is pricey, but lovely.
I think some kind of cover is worthwhile, to protect the screen (mine gets chucked in my bag a lot for when I am hanging about at school collection time, etc). whether you want one with a light depends on you - the screen is not backlit, but then as others have pointed out, when reading a normal book in bed you need some kind of lightsource, so the same source could be used to read your kindle by...