Black Mage Questions

[Sleigh]

"1. Manawall/ward. What's the use of these? I mean, I use them during Ifrit's hellfire etc. But what does it actually block? I know manawall works against pure physical attacks, but is it worth using against special attacks of some HM primals etc?"

Manawall is for when you pull aggro, and for certain specials. Notable ones that get stopped are ADS's High Voltage and Twintania's Divebombs. It's often just used for when you rip aggro, intentionally or unintentionally.
Manaward is for magic attacks, usually for big specials, but it's usually not a big help unless you or your team screwed up (like if Garuda were to have a lot of rocks broken, for example). That said, it can save your life if you know you're going to eat something you can't survive like when you're down on HP.

"2. Aetherial Manipulation. Does anyone use it? I rather run since even if I made some sort of mouseover macro it takes more time to find a partymember ( or hover over the list) then to just activate run and go. Perhaps it is good to use with a focustarget macro?"

The only time I've it in a real fight is back in the early days of Garuda HM, when I got hit by a tornado. It let me get back with my group. Other than that ... never.

"3. Speaking of Focustarget, do blackmages actually need it and what macro do you use for that?"

On PC this is shift+F. It helps for Twintania for her Dreadknight phase, Hydra (I guess), and passing rot. Currently there's not much need to use focus target to be honest, except those examples.

"4. A gear question. Since I know mostly what I want to fill I can manage just fine. However, my girlfriend likes the classical BLM more. That being the Blue garb with the yellow pointy hat. She also likes to carry a shield (although I will be playing with relic+1).
Thus, she want the vanya hat/chest and a Darksteel buckler. I have actually no clue how to optimally meld those though. Anyone have any idea?"

Depends on what you want to do.

If ignoring Coil: Piety until 251 > Determination/Critical Hit Rate > whatever
If going for Coil T1-4: Accuracy until 432 > Piety until 251 > Determination/ Critical Hit Rate > whatever
If going for Coil T5: Accuracy until 432 > Vitality until over 4K HP > Piety until 251 > Determination/Critical Hit Rate > whatever