Wow. This is a big topic.
To deal with the simplest part first - I don’t think you’re going to find any photo-etched aftermarket parts that would be relevant for these models. The sailing ship part of the hobby is far behind the warship part in that respect. In all honesty, though, ships of the fifteenth century didn’t have many parts that could be represented effectively by photo-etched metal anyway.
Different modelers have different opinions about rigging materials. About the only point on which there’s general agreement is - don’t use cotton. It doesn’t hold up will, and it reacts extravagantly to changes in humidity. Some experienced modelers advocate linen exclusively; others (including me) like silk. Both of those materials, unfortunately, are kind of hard to find these days. A good, authentic-looking rigging material that I kind of like is the “cotton/poly mix” sold under the Model Shipways label. You can buy it online through Model Expo ( www.modelexpoonline.com ).
As for sails - now, there’s a really hot topic. We’ve thrashed it out several times in this Forum, and several people have posted interesting ideas and opinions. I think most experienced modelers would agree on one piece of advice: throw out the vac-formed plastic ones that came with the kit.
We had a good discussion of the alternatives in a thread headed “Real cloth sails.” I’ve moved it to p. 1 of this Forum; it should appear on the topic list just below this one.
The appearance of Columbus’s ships is, of course, a matter of intense study and speculation. The bottom line is that nobody knows what they looked like. If you’re interested in the topic, though, quite a few good books have been written about it.
For model builders, the most useful probably is The Ships of Christopher Columbus, by Xavier Pastor. Part of the Conway Maritime Press’s “Anatomy of the Ship” series, it presents detailed reconstructions of all three ships - complete with rigging plans. Unfortunately it’s been out of print for some years, but you might be able to find it in a library or a used book dealer. A good second best is Columbus, by Bjorn Landstrom. I’m afraid it’s also out of print, but used copies are pretty easy to find on the web. Landstrom was a fine researcher and draftsman; his books contain reconstructions that, though not as detailed as Pastor’s, would be of great help in building a model. The general subject of ships of the period is covered in Cogs, Caravels, and Galleons, a volume in the series “Conway’s History of the Ship.” That one is in print; as a matter of fact it just came out in paperback.
For the story of Columbus himself, I continue to recommend the great old classic: Admiral of the Ocean Sea, by Samuel Eliot Morison. It’s an old book, but a thoroughly researched and beautifully written one.
The most popular general book on sailing ship modeling at the moment is Historic Ship Models, by Wolfram zu Mondfeld. A new paperback edition of it just came out recently; it should be fairly easy to find. Mondfeld knows what he’s talking about, and the book is full of useful suggestions for newcomers to the hobby. Its one big weakness is that it’s extremely general in its coverage; it doesn’t go into any depth about any particular modeling project. But if I had to recommend one currently-available ship modeling book this one might well be it.
Hope this helps a little. Good luck. It’s a great hobby.