Wraithknight
1) It is a Gargantuan Creature. No mention on if it is a Lord of War.
2) The Ghostglaive is a Destroyer weapon for the Wraithknight only, meaning the Wraithlord uses the same weapon without it being a Destroyer weapon.
3) All Distortion weapons are Destroyer weapons, meaning that the Wraithcannon, Heavy Wraithcannon, D-Cannon (the artillery unit), D-Scythes and Heavy D-Scythes are all Destroyer weapons assuming none lost the Distort rule.
4) You can legally take up to 12 of these in that new Decurion style detachment via one of the Auxillary formations as you can take 12 Auxillary formations per 1 Core formation, basically rendering a Lord of War positional change pointless.
5) It still has 6 Wounds - the Bloodthirster of Insensate Rage "half kills" it and is specified to do 3 Wounds to it.
6) It is not Initiative 1 either base or with the Ghostglaive, it strikes after the Initiative 9 Wrath of Khorne Bloodthirster but before the Initiative 1 Bloodthirster of Insensate Rage. It is most likely still Initiative 5, making it even scarier than an Imperial Knight in combat.
7) In the "battle report", it takes on both of those Bloodthirsters and wins, it beats two Toxicrenes, then it pulps an Imperial Knight and a Transcendant C'tan in separate conflicts. It gets stomped by Deathwing Knights in Smite mode, however.
Windrider Jetbikes
1) They are exactly the same in terms of stats, special rules and so on; they are still 3+ armoured Eldar with Ballistic Skill 4 and the usual Eldar Jetbike rules. They are a Troops choice.
2) Each Windrider can take a Scatter Laser or Shuriken Cannon, not 1 in 3 like the old codex. Yes, this is as bonkers as we all initially feared.
3) Warlocks can now be purchased as part of the squad rather than having to purchase a Council and splitting them off as before. We can expect the same thing to happen with Guardians.
4) Ancient Doom and Battle Focus are still present, though any changes to either are unconfirmed. We can all hope that Battle Focus actually works for everyone that has it now, including Jetbikes.
5) Bladestorm is exactly the same as it was, as we all knew from the Harlequin codex.
6) All of the guns appear identical, save that the Scatter Laser no longer has the Laser Lock special rule.
7) Warlocks can only take Sanctic Daemonology and Runes of Battle. This might indicate that Eldar have a similar rule to Grey Knights where they can safely use Sanctic Daemonology but can never use Malefic Daemonology.
"Decurion" Detachment
1) Eldar have their own version of this, featuring Command, Core and Auxiliary choices. You can take 1-3 Core choices (all of them are Guardian themed, one being Jetbike oriented and all requiring one Vyper), 0-3 Command choices per Core choice and 1-12 Auxiliary choices per Core choice.
2) Wraithknights are part of two separate Auxillary choices, and as Auxiliary choices are 1-12 per Core choice, you can legally take 12 Wraithknights per Core choice as mentioned above.
3) The "army-buff" as per the Decurion is specifically related to mobility, though whether it will be solely tied to Battle Focus (seems to be the implication) or will just affect all units remains to be seen.
Additionally, the codex is indeed 160 pages. We seem to be getting some kind of special bonuses related to each Craftworld, but this isn't specifically outlined. Whether or not we get Craftworld rules ala Space Marine Chapter Tactics remains to be seen.