A good place for students of this period in the history of shipbuilding to start is Cogs, Caravels, and Galleons: The Sailing Ship 1000-1650, edited by Richard W. Unger. It's a volume in the series Conway's History of the Ship, and is an excellent introduction to what is known - and not known - about European ships of the era.
I can't answer all of Publius's questions, but I can pass on some information about the various Revell kits. (My source, as usual, is Dr. Thomas Graham's fascinating book, Remembering Revell Model Kits. I believe somebody published a similar book about Heller, but I've never seen it; I have the impression that it only got limited distribution - and virtually none outside Continental Europe.)
Revell's original Santa Maria was first released in 1957. It's been reissued many times. So far as I can tell it's always maintained its original name. (Heller did issue at least one other kit, under the name "Conquistador," based on its Santa Maria kit - but I don't think Revell did. I could be mistaken about that, though. Dr. Graham's coverage stops in 1979, and Revell has done quite a few odd things since then.) Our knowledge (or lack of knowledge) of Columbus's ships is such that it's hard to pin down exactly what scale the kit is on. But if it's 1/90, those beautifully-rendered crew figures must represent midgets.
According to Dr. Graham, this was the third sailing ship Revell produced. (The first two were the U.S.S. Constitution and H.M.S. Bounty, released in 1956. The Santa Maria and the Flying Cloud appeared the next year.) The lack of planking detail inside the bulwarks is fairly typical of kits from that era. They were designed in such a way that most of the detail work was done on one half of the mold. I suspect the "seams" between the "planks" are indeed too wide, but there's room for debate there. We don't know much about Spanish practice in 1492, but in later years it was routine practice in wooden ship construction to bevel the edges of hull and deck planks in order to produce a relatively wide grove between them on the exterior surface. The caulker would then do his job of pounding caulk into the seam; the result kept water out more effectively than wood-to-wood joinery would. But if memory serves (as it frequently doesn't these days), the Revell designers probably overdid the effect a bit.
One thing that baffles me about that kit is the way the flags are represented. Some excellent draftsman apparently spent a great deal of time drawing them as representations of flags rippling in the wind, with the "ripples" drawn in perspective. As drawings they're remarkable - each is designed to be folded over in the middle, and if the modeler does that carefully the "ripples" will line up perfectly. But why fasten a two-dimensional flag, drawn in perspective, to a three-dimensional model? Viewed from any angle but the right one, those things look utterly ridiculous. Life would have been far easier for the artist if he'd drawn the flags "flattened out" - and any model builder who's capable of dressing himself surely can put genuine, three-dimensional ripples in a flag in a few seconds. That tradition of "rippled" flags was a hallmark of Revell ship kits for many years.
Two of Revell's last sailing ship kits were the Golden Hind, originally released in 1965, and the Mayflower, originally released in 1966. They are completely different kits; I believe the only parts they share are some rigging blocks (which were recycled from the old Cutty Sark kit). The Golden Hind and Mayflower are, in my opinion, two of the best kits Revell ever made. Both are reconstructions; the documentation about the two ships themselves is almost non-existent. The Golden Hind kit appears to be based on a set of reconstructed plans by a German author named Rolff Hoelker (I may have misspelled him) back in the 1930s or 1940s. The Mayflower kit is in fact a scale model of the full-sized replica Mayflower II. The latter was designed in the 1950s by William Baker, Professor of Naval Architecture at MIT.
Both Hoelker and Baker quite obviously made extensive use of a set of documents called the Matthew Baker Manuscript, which is in the library of Cambridge University. It dates from the reign of Elizabeth I, and the drawings in it are generally regarded as the oldest surviving plans of English ships. Virtually every other author and model builder trying to reconstruct a ship of that period has relied on the Matthew Baker drawings.
William Baker concluded, on the basis of the very scanty written evidence, that the original Mayflower was a pretty old ship when she sailed for America in 1620 - old enough for the Matthew Baker drawings to be applicable. In recent decades other researchers have come up with other interpretations of what both the Mayflower and the Golden Hind may have looked like - but the bottom line is that nobody knows for sure. My opinion is that the Revell reconstructions still hold up pretty well, and both kits have the potential to be turned into excellent models.
Revell, like Heller, is notorious for getting the most possible use out of its molds - and letting history take a back seat to merchandising. According to the list of kits in the appendix to Dr. Graham's book, the Golden Hind kit got reissued under the names "Spanish Galleon" (1974 and 1978) and "Pirate Ghost Ship" (1978). Revell also had some sort of relationship with Heller for a while; the Revell Golden Hind seems to have appeared under the label "Corsair," or something similar, in a Heller box. The real Golden Hind was no more a Spanish galleon than the U.S.S. Kidd was a Japanese battleship. (To begin with, the word "galleon" by definition refers to a big warship. The Golden Hind was a tiny vessel. And though our knowledge of Spanish shipbuilding in the sixteenth century is extremely sketchy, the hull form of that kit is quite distinctly English.) The "Pirate Ghost Ship" was molded in some sort of green plastic that glowed in the dark. Great.
The Mayflower kit, with a few parts changed or added, was reissued in 1977 under the name "Elizabethan Man-O-War." That label is easier to swallow; it's possible that a ship that looked like that did exist during the reign of Elizabeth I. But anybody who's familiar with the subject can see at a glance that it's a model of the Mayflower II.
I've often wondered what the skilled artisans who did the actual design work on the original kits thought when they saw their work being marketed in such ways. It's also occurred to me that in almost any other field of enterprise, such stunts as those pulled by Heller and Revell would be regarded as deceptive marketing and subject to lawsuits.