Just start using this 16 GB version N9. You can always sell later your used 16gb phone and buy used 64gb one.

About colors - brand new black device looks the best. However, after 6 months usage paint / lacquer starts to come off. Only casing that does not have such problem is white one as it is made of plastic and not polycarbonated as the other colors.

This is a reason why I changed my black casing to white one - black one started to look weared out and ugly.