I'm sure Bill is as aware of this as I am, but the hull of the Preussen was not copper sheathed. Two reasons. First, by the time she was built, in the early twentieth century, anti-fouling paint had been perfected to the extent that it was more effective than copper sheathing. Second, her hull was made of steel, which is just as resistant to marine life as copper (probably more so).
To be really accurate, the hull below the waterline should have indications of the edges of the steel hull plates on it. I don't remember whether the Heller kit shows the plating above the waterline or not; in any case, the above- and below-waterline portions should look the same except for color. Maybe Bill's suggestion was intended to imply using copper tape or sheet styrene as the basis for a coat of red paint; come to think of it, I guess that would work - but it wouldn't be easy. The compound curves of such a ship's underwater hull are pretty hard to cover with such materials, and getting the layout of the plates on the port and starboard sides would, I suspect, be even tougher.
I've never built a sailing ship of that period, and it's been a long time since I've read much about such vessels. My recollection (which may well be defective) is that the big German windjammers generally were painted in a two-tone scheme below the waterline: dark, slighly rusty red for the ship's bottom, and a broad band of dull pink (yes, pink) from the waterline itself to several feet above and below it. I'm anxious to be corrected if my memory on that point is wrong.
If I were building such a model the first two sources I'd read would be a pair of books by Harold Underhill: Deep Water Sail for the basic characteristics (including color schemes) and Masting and Rigging: The Clipper Ship and Ocean Carrier for the spars and rigging.
Regarding the Star of India - I agree that she would make a beautiful model and a good subject for a plastic kit. Unfortunately, though, the number of plastic sailing ships is, compared to the coverage of aircraft, tanks, and even twentieth-century warships, almost microscopic. The number of attractive and important sailing ship subjects covered by the plastic kit manufacturers is far, far exceeded by the number that haven't.
Youth, talent, hard work, and enthusiasm are no match for old age and treachery.