Wearing
exactly four pieces of the Ahzidal set will net you +10 Enchanting skill, like SilverFerret said. Wearing five pieces will not give you the bonus, and you have to wear the boots to get the bonus. Also, the Ahzidal dragon priest mask counts as part of the set. The effect is called "Ahzidal's Genius" and can be seen in your active effects list. This doesn't boost items that are already enchanted, only items that you enchant while wearing the gear.
Another new bonus for Enchanting is the Seeker of Sorcery ability, which increases Enchanting by 10% and is granted by the Black Book: Sallow Regent (found in White Ridge Barrow IIRC). You can also improve Alchemy by 10% using the Seeker of Shadows ability, and Smithing by 10% using the Seeker of Might ability. But keep in mind you can only have one of these three abilities at any given time, meaning to get the maximum out of your crafting skills you will have to go to Apocrypha and switch between them a lot.
As for the new cap on looping Fortify Alchemy and Fortify Enchanting, see this copypasta from a post I made elsewhere:
The new cap [for looping Enchanting potions and Alchemy enchants] without exploits (including Necromage Vampire and Falmer Helmet as exploits) is 35% for Alchemy enchantments. Smithing, Destruction, Light Armor, etc. are all the same magnitude. So yes, you can now legitimately reach 100% cost reduction with only 3 enchantments.
To get this high, you'll have to create a Fortify Enchanting 40% potion, have Seeker of Sorcery active, and wear exactly 4 pieces of the Ahzidal set (one must be the boots).
For those interested, Magicka/Health/Stamina enchants with this setup come out at 88 points. Fortify One-Handed/Two-Handed/Archery/Sneak enchants come out at 57%. Resist Fire/Frost/Shock come out at 66%, but that's with the elemental perks in enchanting.
I should also mention that to make a 40% fortify Enchanting potion, you also need to use Seeker of Shadows. This means every time you make a potion you'll have to go to Apocrypha and switch abilities, then switch back before you enchant your gear. If you don't do this, the highest enchanting potion you can make is 39%, and your Fortify Destruction enchants will be at 34%. Still able to reach 100% cost reduction with three pieces.
If you do use the Falmer Helmet exploit then you'll get higher numbers since it lets you make stronger Enchanting potions (the reason the above poster didn't get higher numbers is likely because they did not use Seeker of Sorcery). And you'll get much higher numbers if you're a Vampire and have Necromage. But I didn't test those, so I don't know the exact magnitudes.