dslrdashboard.info

With the camera built in wireless you can only connect to one camera.
Eventually you could use a portable wireless router or a Raspberry Pi running ddserver. Connect the cameras with USB to it and you controlling device with wireless to it.

Yes the Z5 is also supported.

You can use it on multiple devices as long you use the same Google Play account that made the purchase.

What camera did you use?
What where the exact settings? Maybe a screenshot.

If it does not support the 'Smart remote control' Playmemories camera application then it will not work.

- enable wireless on your D7500 - connect your Pixel wireless to the D7500 - start qDslrDashboard and press the 'Nikon wireless' button * be sure that no other device is connecting to the D7500 wireless * be sure that the Nikon WMU or Smartbridge applicaitons are not running on your Pixel * be sure ...

No it is not, on iOS devices only wireless connection is possible.
USB is available on Android and the desktop version (Windows, Linux, macOS)

You should long press the qDslrDahboard capture button after it will turn red, after that the image is downloaded after the capture.

You can download the images from camera SD card in the qDslrDashboard 'Image gallery'.
Not sure if that is what you mean.

On what platform do you use it? Please contact me with the support email.