WinterH

Aside from maaaybe F-4s during Vietnam, I don't think Zunis were used on any USAF aircraft, they are really a NAVY/USMC weapon. Although I think some export customers did get them for aircraft made for USAF and didn't use them there.
As for the A-10, can't say I have any primary source info to prove this, but I doubt they were ever a thing on A-10. They may have been tested before A-10 going into service maybe, at most.

You command the other seat's actions through various simple "AI" interfaces. Look up George AI, Petrovich AI, and Jester AI to see how they are implemented on AH-64, Mi-24, and F-14 respectively.

Missile exhaust ingestion causes engine stall now since BS3 update. You need to fire them from at least around 120 km/h forward speed.

You don't move TADS with cursor control, but with manual targeting thumb controller found on the right handle of TEDAC. Select TADS as the active sight, unless it is slaved to an acquisition source you should be able to move it around. If it is slaved, pressing the slave button will let you slew it.

Ballistic limit afaik. So the weapon is out of range.

Yes, if you choose any acquision source for your current sighting system, pressing the slave button will make your sight target whatever that acquision source is, which can be a waypoint/target point, pilot's or gunner's helmet, and I guess in future the radar.
To get your human gunner to see where you are looking at for example:

- Pilot looks at the target area, and tells CP/G to slave there
- CP/G chooses pilot helmet as the acquisiton source for TADS
- CP/G presses slave button, which will slave the TADS to wherever pilot is looking at
- CP/G presses slave again when he wants to slew around the TADS to look for targets there.
Similarly, as the CP/G, if you choose TADS as your targeting system on the right handle of TEDAC, TADS video will overlay on your monocle display. Then, choosing gunner helmet as your acquision source, and pressing slave will make TADS follow your head movement, and you can "see through" the helicopter with FLIR or TV, but you can also zoom on that overlay. When you are satisfied where your TADS is looking at, press slave again, and fine tune with slewing control on the right handle of TEDAC, probably also turn the monocle off, as I personally find it distracting after finding the correct area.

DIAFR OPEN switch, to the right of observe switch on the sight switchbox in gunner's cockpit. Some weirdness will follow though, at close ranges a hit is unlikely, and from a low altitude, or with lots of obstacles around like buildings/trees/powerlines, missile may hit them before it's reined in by the guidance. But, the option is there.
 
Another option is to fire the missile directly ahead, and then bring it smoothly down onto target, and this is apparently done IRL by operators as well. Takes some skill though.
 
So YoYo is partially right, Mi-24 doesn't particularly like attacking from hover like most helicopters, it can only hover when it is light, not at high altitudes, and it isn't too hot, and it can get more wobbly than what the sight gyros can handle when doing that, so it's extra workload on the operator with still a decent chance to miss. But, it is possible, and right now you have at least two different ways of achieving that. Now, I don't know if DIAFR OPEN thing is realistic, or something that will get removed in future with a fix, but it is possible to use it as a launch authorization override now.
 
Finally, these only work with a human in the operator seat, if you are working with Petrovich as operator, you will need to follow the actual intented method for the Hind, and align the boresight with the missile sight, and fly towards target.

By default, either with Left Alt+C or double click with middle mouse button. At least as far as I recall, that is.