1/ As far as physical strength and endurance goes, the upper limit is probably Fingolfin's battle with Morgoth:
But at the last the King grew weary, and Morgoth bore down his shield upon him. Thrice he was crushed to his knees, and thrice arose again and bore up his broken shield and stricken helm. But the earth was all rent and pitted about him, and he stumbled and fell backward before the feet of Morgoth; and Morgoth set his left foot upon his neck, and the weight of it was like a fallen hill. Yet with his last and desperate stroke Fingolfic hewed the foot with Ringil, and the blood gushed forth black and smoking and filled the pits [left by] Grond. ('The Silmarillion', Chapter 18)
Morgoth, at this point, is huge - he's described as a like a tower, or a stormcloud. But Fingolfin not only survived - and got back up from - three blows from this giant - he also survived having Morgoth step on his neck long enough to cut his foot, and deeply. So that speaks well for both strength and endurance.
Switching to the Third Age, we find Legolas wanting to keep running in Rohan after a full day, when Gimli is exhausted (and ignore what the movies say: dwarves are quite clearly built for endurance). He was also the only one not borne down by the troubles on Caradhras - though that might have been more to do with being able to run on top of the snow.
Switching to another famous elven ability - sight - there's a lovely article which goes into detail on that. Suffice to say that Legolas would be able to notice within under ten minutes the motion of Mars against the starfield - a human would have to wait ten hours.
2/ "... this is what your folk would call magic, I believe; though I do not understand clearly what they mean; and they seem to use the same word of the deceits of the Enemy. But this, if you will, is the magic of Galadriel." (LotR II, Chapter 7)
I'm glad you're not asking about all magic in Arda - that one's a really tricky subject. But as to the elves, there are... maybe five kinds of 'magic':
a) The Light of Valinor, as seen on Glorfindel in Fellowship. This is a byproduct of having lived under the light of the Trees, and is basically an 'inner light'; in the Unseen realm, it manifests as an almost blinding glow, and is at minimum terrifying to Nazgul. Obviously, it's only present if you, uh, lived in Valinor before the Trees were murdered.
b) Foresight and Insight, or to give them their proper names, apacen and tercen. These are pretty much what the sound like - apacen is the kind of future vision Galadriel obtained through her Mirror, and tercen is her... semi mind-reading. She may or may not possess actual telepathy as well, I don't think that's made clear.
c) Craft. Elven-work is, um, better. ^^ Ringil, the sword of Fingolfin, wounded Morgoth eight times, while a Numenorean blade dissolved after stabbing the Lord of the Nazgul just once. Furthermore, elven-craft can enhance the properties of objects above what is natural:
"Are these magic cloaks?" asked Pippin, looking at them with wonder.
"I do not know what you mean by that," answered the leader of the Elves. "They are fair garments, and the web is good, for it was made in this land. They are elvish robes, certainly, if that is what you mean. Leaf and branch, water and stone: they have the hue and beauty of all these things under the twilight of Lorien that we love; for we put the thought of all that we love into all that we make..." (LotR II, Chapter 8)
A few pages on, we come across Galadriel's gifts: at a minimum, the Phial of Galadriel is enhanced, and quite possibly the earth in Sam's box as well. The boats, the ropes - even the lembas of the Galadhrim is 'magically' enhanced.
But this enhancement isn't 'add any attribute you like'; it seems to only make things more themselves. The cloaks, woven light and camoflaged, become extra light and super-camo. As to how this was done...
d) Song. Don't knock singing - it's the very method of the creation of Arda. And it's most definitely a tool of elvish magic:
And Luthien now was left alone.
A magic song to Men unknown
she sang...
... and all names of things
tallest and longest on earth she sings:
the locks of the Longbeard dwarves; the tail
of Draugluin the werewolf pale;
the body of Glaurung the great snake;
the vast upsoaring peaks that quake
above the fires in Angband's gloom...
Song is the medium by which Luthien enhances her craft - in this case, she's imbuing her own hair with the properties it already possesses: length, and darkness. When she's done, she has enough to weave a cloak and rope, and darkness/night enough to bring down sleep on anyone she chooses - up to and including Morgoth.
And music isn't just used in craft (or by half-Ainur): the most famous passage from the Lay of Leithian runs, in part, as follows:
He [Sauron] chanted a song of wizardry,
Of piercing, opening, of treachery,
Revealing, uncovering, betraying.
Then sudden Felagund there swaying
Sang in answer a song of staying,
Resisting, battling against power,
Of secrets kept, strength like a tower...
Here, both Sauron and Finrod (Felagund) are trying to enchant not an object, but a person - Finrod himself. Sauron uses 'the deceits of the Enemy' - Finrod, in contrast, tries to enhance his own nature. He fills his song with resistance, with 'trust unbroken', and with 'all the magic and might... of Elvenesse'.
Ultimately, he fails, because Sauron turns his own song against him: he twists Finrod's memories of 'the sighing of the Sea beyond/Beyond the western world, on sand/On sand of pearls in Elvenland' with the reality of the murder of the Trees, and of Feanor's kinslaying.
The wolf howls. The ravens flee.
The ice mutters in the mouths of the Sea.
The captives sad in Angband mourn.
Thunder rumbles, the fires burn--
And Finrod fell before the throne.
But still - I'd love to see a story about elven battle-song. ^^
(All of which suggests a new spin on Galadriel's 'Namarie', which ends with her singing: 'May it be that thou [Frodo] shalt find Valimar!' Poetry, a hope, a wish - or an enchantment and a spell? You decide.
e) Illusion. This one shows up mostly among people who knew Melian. She, of course, spun a web of illusion and magic around Doriath, to keep unfriendly creatures out. Later, Finrod used similar illusion - 'by the arts of Felagund their own forms and faces were changed into the likeness of Orcs'. And waaaaay down in history, Thranduil (whose father was a member of Melian's court) apparently uses something related to spirit his feasts away from Thorin's company.
But all of these sort of fall under 'craft'. Finrod had to outfit his party with Orcish gear and weapons, which he could draw on the essence of; Melian used the already-tangled woods of Doriath; Thranduil had Mirkwood to draw on. The idea that an elf could, say, create an illusion of an elephant, is unsupported by the Legendarium.
f) [Okay, I lied, there's six] The Rings. I've discussed this on Netilardo. The evidence suggests that the Three Rings were created to sustain the world, which is what Galadriel uses Nenya for. (We can ignore Gandalf's apparent use of Narya - he's a Maia, there's different interactions there). And apart from communicating with the wearer of the One Ring, that's all they're for: freezing time in place, so that the world of the Eldar doesn't pass away.
3/ Galadriel, Thranduil... yipes. Well. Galadriel is a warrior, so she could be enhancing her 'scary' aspect... nah, sorry, I think the best explanation for that is 'PJ doesn't know what starlight looks like'. The book describes starlight in the scene by the Mirror, and her 'Storm Queen' scene in B5A would also make more sense with starlight (known for its evil-banishing properties). Actually, I'd swear I saw her holding the Phial in that scene - I wonder if the Dark/Evil/Scary thing was added in post-production.
Thranduil is much easier: movie!Thranduil was supposedly scarred by a dragon, but we've already established he could have access to 'enhancing' illusions. The illusion of your own face being undamaged must be quite simple.
4/ I think most of this has been answered above. There's no fundamental differences between the tribes of the Quendi - the only determining factors are: whether they saw the Trees in their glory, whether they knew Melian, and whether they have a Ring. Galadriel, of course, fulfils all three - and she and Celebrimbor are the only people in history to have done so (and 'Brim may never have met Melian).
This has been your overly-long answer to a Tolkien trivia question of the week. ^_^ Well, you asked!
hS
