At the risk of repeating myself,...I'm going to repeat myself. The word "never" there actually did mean never. You don't ever have to do any of that. The battery will take care of its own temperature always. There are some little benefits you can get if you want to, but they are never necessary.
That thing with the i3 is the same as with any electric car. If it's starting off really cold, it's just going to take a lot of extra energy at the start to warm things up, including the inside of the cabin. That's not bad at all for the car, but that's going to use up some extra driving range. In a short range car like the i3, that matters, but in a long range electric car--not so much.