World quests in general are going to be good for raid prep/suplement in the first 3 months. I think the items will go up to 850, and you can also get relics for your off-spec weapons, which was nice on beta. The mega-world quest daily (requires 4 world quests tied to a faction) will give you a box with random shit in it, including a chance at a legendary, and 500 rep with that faction. These dailies can stack up to 3, so, at least every 3 days, you should do 12 dailies, which are fairly fast.
World quests are also the only way to get the new garrison (class hall) resources at 110, that I found. You will need truck loads of them to max out the class hall and enable the use of 2 legendaries at a time.
For trade skills:
Gathering profs are easy to get to 100 getting legion mats, that you need to gather anyway. The skill 100 cap only applies to the world quests, and you should be able to bang out that skill in a couple hours. The world quest is the only place, currently, where you can get the green gathering mats (such as
Felwort - Item - World of Warcraft).
Production professions should be likewise, easy to get to 300, granted you have the mats. Each combine will give 3 to 5 skill points, and there is no reroll token, like in WoD. So you will need to keep making items to get the optimal stats. You need a plethora of trade skill items, just to eat at the forge, to eventually make the upgrade tokens. Those tokens take the item from 815, to 850, 5 ilev at a time. World quests can give rank 2 recipes. I didn't see much else, as rank 1 seems to be tied to quests, and rank 3 look like they are on faction vendors.
Some items do require skill 800, like a few gems and the alchemy caldron. I have not found many needing 800, but you will need to look at the wowhead guides, as the in game interface doesn't seem to list skill needed. If you dont think you are going to make a bunch of legion items, before you need the skill level 800 stuff, then by all means, use WoD to level up. You can gather your own mats in the garrison, fairly easily.
Here is how the
Obliterum works:
(I cant get the wowhead links to give a pop up window and link properly, so this will look a little messy)
There is a quest (
Fire! - Quest - World of Warcraft) you get at 110, that leads to 7 more quests that will eventually unlock the Obliterum forge. Note:
Trial By Fel Fire - Quest - World of Warcraft requires 1 bracer from blacksmithing, 1 from tailoring and 2 from leatherworking.
Each crafted item gives a set amount of
Obliterum Ash - Item - World of Warcraft.
-Legs give the greatest return on invested mats at 20
Obliterum Ash.
-You need 100
Obliterum Ash to turn it into
Obliterum - Item - World of Warcraft.
You need 7
Obliterum to make an item 850 ilevel.
So, 1 item to ilevel 850 needs 35 legs, and making 35 legs gives 175 skill points.
Edit: Forgot some smaller combines (like bracers) give less skill points