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So far I have had good luck with these sensors. I've been using the serial data with an old school serial to USB adapter into the laptop for logging with COBB or Romraider. I've always had good agreement between the factory O2 sensor, the AEM wideband gauge, and the logged AEM wideband data.

The only difference between those two sensors is the length of the cable.  

I just had to fix this last weekend. I set both driving and driven speed source to the same input and it worked immediately. 

Yes, the 5v sensor supply & sensor ground can be shared between multiple sensors.

You don't have to connect up an output from the sensor to the ECU if you don't wish to.
I have a combined sensor in my fuel pressure regulator, but I'm only using the Pressure side, so I have connected 5v, sensor ground, and the pressure output to the ECU.
So, yes, that's correct

It will be fine connected to the ecu ground.  

Yes the JST plug on V1.4 Subaru V6 pnp bottom boards matches the above and can be used to power things including CAN Lambdas. Note Haltech doesn't necessarily use the same pinout as the Link CAN Lambda and so some re-pinning of the connector may be required.

It doesnt look like you have done the cam angle calibration.  Run the engine at fast idle and set the cam angle test to calibration, it will populate the tooth offset table then turn itself back to off if successful.  Cam position should be working then.  I would also suggest you set the RPM lock out and ECT lockout to something more appropriate.  Usually around 1200RPM where there is stable oil press and around 60°C where oil viscosity is starting to become thin enough to work.  

I have the Haltech CAN protocol document.  Attach your ecu map and I will set it up.

I agree compelely with @koracing - sell that AEM gauge off to some other unsuspecting person who won't ever be hooking it up to an ECU, and get a Link CAN Lambda module ASAP.
 
I honestly spent days fiddling around, tuning and retuning the same areas of the table over and over as it would be totally different day-to-day with no other changes. (I'm just doing road tuning with log files/mixture map mostly). Once I switched to the Link module, I wasn't changing the same cells over and over each time, each drive had fewer and fewer changes to incorporate, and it ran much much better.
If you're paying for dyno time and expecting the ECU to work well, it's a waste of money not just buying the right bit of kit ASAP and trying to "make the most" of the rubbish you've currently got.

Personally I wouldn't let a 7 year old wideband put your 2023 tuning efforts at risk.

It's also likely to change every time you drive the car, too...  I spent days chasing my tail with it, until I ripped it out and replaced it with a Link CAN Lambda.

The 30-4110 doesn't have a ground reference on the analog out so there's usually some offset.  Like Adam said you'll need to make sure what you see on the gauge is also what you see in the ecu.  

You can use any brand of wideband controller, so long as it outputs an analogue signal, or via CANBUS and the protocol is known.
However, the Link one is one of the best in my opinion. It talks bi-directionally to the ECU, doesn't heat the sensor until the car is running (prolonging sensor life), informs the ECU if it detects any failures, is a fully digital signal, so no conversion inaccuracies, very quick (I think I read here it transmits 100 updates per second, it certainly updates the values very quickly).
 

DBW will be dependent on board revision.
AVCS, oil and fuel pressure shouldnt be an issue once you shuffle the I/O around.
Turbo speed will work if you get a frequency divider as it will get higher than the digital input will allow.

You can use VVT (AVCS) on auxs 1 to 4 and vvt sensors on digital inputs 1 to 4, so you might need to move other functions off those pins. 
 
No, you can not reassign inputs to outputs or digital input to an analog input, you will need to repin.  You can however reassign an analog input to a temperature input (you will need to add a pull up resistor as only temp. Inputs have these internally.) 
 
HTH, 
Richard.