As far as I know, My Immortal is off-limits because someone's claimed it. That's what the wiki page says... but I can't find anything by some quick searching. Eh.
Anyway! On to interesting stuff, and Question the Third:
a) Dreams, dreams, dreams... a claimed dream-warning will be treated with both more reverence and more suspicion. Dreams are the favoured prophetic method of the Valar; Ulmo sent dream-messages to Finrod and Turgon (leading to the founding of Nargothrond and Gondolin), for instance. But... the Valar don't get involved much these days, and Amy has never been anywhere near the Two Trees (which might help make her easier to communicate with for Lorien or whoever). That said, note that Frodo dreamt of Gandalf in Bombadil's house - the dream was late, according to Gandalf, but it's still a dream-vision (and Gandalf never doubted it).
b) Glorfindel is actually a perfect choice - not only is he a de facto Seer in his own right, he's also spent time around at least four others: Malbeth (this is an assumption, but I think a solid one), plus Turgon, Idril, and Tuor, all of whom had visions or other messages involving Gondolin. If there's a pattern in how those messages were presented (and it's very hard to say, since the only two we have details for are Turgon and Tuor), he'd look for that pattern to be repeated. If not... 'feel', probably.
c) Uh... not that I know of? ^_^ I'm pretty sure alchemy isn't mentioned by Tolkien; looking at the stars might be, I honestly don't know. I do know that early descriptions of Numenor imply it reached an Industrial Revolution stage of technology: Our ships go now without the wind, and many are made of metal that sheareth rocks, and they sink not in calm or storm; but they are no longer fair to look upon. But our shields are impenetrable, our swords cannot be withstood, our darts are like thunder and pass over leagues unerring. But I don't know anything about prophecy.
Actually, that's a lie: the Druedain (aka the Wild Men met by the Rohirrim on the way to Minas Tirith) lived on Numenor, and left centuries before the Downfall, since (they claimed) the island felt unstable. So there's that.
hS, rambling.