Welcome new Zelda player!
To answer your first question: Zelda's specials are either amazing or mediocre in this game. You didn't mention upB so I assume you know its general uses. Just remember that it combos into itself and can kill a lot of opponents around 70-80%. As for Din's Fire, this move is usually regarded as useless among most Zelda players. It's a pretty good edgeguarding move to keep a recovering opponent on their toes and can be used as a mix-up on projectile based characters. It's especially useful against characters that like to sit at the edge and charge stuff up like Samus and Robin. Keep taking chip-shots at their shields with Din's and they'll feel the urge to approach you most of the time. Do not overuse Din's though as, again, it really isn't that great due to its predictability. Zelda's phantom is still pretty undiscovered territory for Zelda users since it's a brand new move and uses newly introduced mechanics such as walling. It's most popular use is for edgeguarding as it will rush out beyond the ledge to catch people that are recovering high and will usually kill them from that far out. However, a smart player will usually discover what you're doing if you constantly use only phantom to edgeguard so mix up phantom, Din's and dair to keep the opponent guessing at what you're doing. Since the opponent ought to be recovering low (because of phantom) this gives you a great opportunity to go for a dair spike. As for Nayru's Love, it's Zelda's best OoS option unless you are looking for a kill, in which Farore's Wind is what you're looking to use OoS. Nayru's has a few frames of invincibility on it so it's relatively safe to use when the opponent unsafely approaches you (especially when the opponent goes for a grab. The invincibility frames mean no grab for them and free damage for you). The other main use is as a reflector but remember to use it sparingly since the endlag can be a hindrance. These aren't her only options OoS obviously. Her shield grab is significantly better in this game than it was in brawl because it's no longer a tether grab so it's a lot faster. Zelda can also string moves together on a dthrow or uthrow now such as nair and uair and even bair or fair if the opponent DI's left or right. Throw strings will probably be your most consistent damage as Zelda next to good reads/punishes.
To answer your second question: Zelda is outcamped by characters like Link/Tink, Samus, and Duck Hunt. Using Nayru's Love against them can help but isn't always the best option since a smart player will usually snuff this strategy out and begin baiting you into using it. One strategy that has helped me a lot against spammy campers is to full hop towards them while charging a phantom, release phantom when you are near the stage (this will block the projectiles the enemy throws at you) and use Din's from behind your new cover. You can also use an uncharged phantom to absorb one small projectile if you need it quickly. What you'll want to keep your eye on is when the opponent uses a laggy projectile move. For example, Robin throws out Arcfires a lot but it has quite a bit of endlag on it. Recognize how many frames of endlag he has and use Farore's Wind while he's vulnerable. Link's/Tink's boomerang as well as Samus' missles and most of DH's projectiles also have quite a bit of endlag which you can exploit with Farore's Wind. Basically, you teleport right behind what they want to use to keep you out, disregarding the camper's strategy altogether and getting a sweet 7-14% or a kill out of it depending on how high they are.
Megaman is a lot trickier because he can throw so many projectiles at you in such a short amount of time. Also, reflecting most of his projectiles won't do you any good because Crash Bomb and Saw Blade will despawn before they even reach him giving him a free punish off of your Nayru's lag. Using Nayru's here is risky so use it sparingly. Farore's is also trickier than the other super campy characters since MM's endlag on his projectiles isn't nearly as significant as the others I've mentioned so work on your timing in punishing his projectiles, you have a shorter window for this in general compared to other campers. The only other camper that should be giving you any significant trouble is Villager because reflecting his Lloid Rocket and slingshot rocks will be useless as they'll either despawn before they reach him or will collide with his tree that he should have up if he's spamming projectiles. The key here is Din's Fire since he can't pocket it and it will go through his tree meaning his cover doesn't actually do him any good typically forcing him to come out from behind his tree and fight you like a man (not to mention, if he cuts it down, you can just reflect it back at him for a very satisfying kill). This MU requires a lot of patience since Villager will always be trying to wall you out with Lloid Rockets and fair/bair. Powershield these while walking towards him to learn his patterns and punish him when he slips up or continues an easily punishable pattern (Ex: SH fair-->SH fair-->SH fair. Farore's Wind at the right time to teach him a lesson). DO NOT USE PHANTOM AGAINST VILLAGER! This is suicide.
To answer your final question, I'll point to my comments on Zelda's specials since they are almost solely edgeguard options with a few exceptions. Zelda's dair is the best meteor smash in the game next to Ganon's so use it. It'll net you kills as early as 20% on some characters (especially Lil' Mac). Also, remember that Zelda has plenty of multihit moves so an opponent trying to get back onto the stage from the ledge should find it pretty difficult since Zelda's fsmash/Nayru's love will do really well against rolls, hops, and plain getups while a jump from the ledge is deadly considering Zelda's bair, fair, and uair are all potent kill moves. Just a note about Phantom here: It can hit an opponent that is hanging on the ledge without invincibility frames when it's fully charged. Basically, when the fully charged phantom stops moving and sticks its sword out, the very tip of the sword should be right above the opponent's head for it to hit them. It's really tricky spacing and situationally useful but can take your foe by surprise.
Sorry for the wall of text but I hope this helps you in using our beloved princess!
