I can't really say that you should buy this quantity and this color, honestly it would be triple hard to say exactly how many. You could probably start with one for each :)
Or you could either have all sizes for each color/style. If you can't spare that much you can have 1 color 1 size.
In situations like these, dropshipping really makes everything so much simpler since with dropshipping you can offer the full range without having to worry about any unsold stocks!
Sorry I was not of that much help here.. but I do wish you all the best in your business!