You can always scale them to fit the zero to one space. I wouldn’t call it necessary, but it is better if you used all the texel density available in your space. It is wasted if you leave your islands small and then your texture will be lower resolution that it should.
You don’t need to move the islands, the packing algorithm will move them for you in the end, so I’d say it doesn’t matter where you place them if you’re going to pack them.
