I use this selfie stick with my iphone 6s plus and am very satisfied!

1. the feet can be moved individually, but they do not lock in place, so there are no intermediate steps, only open and close. Uneven surfaces can only be compensated for to a very limited extent. In addition, the feet are quite thin and only 10 cm long, so the whole thing is a rather wobbly affair and rather top-heavy, probably also susceptible to wind. At least you can unscrew the feet if they get in the way. The shutter release has one button for Android and one for iPhone. No app is needed for the iPhone. After pairing, one press of the button activates the camera shutter if the camera app is open AND in the foreground. Otherwise, pressing the button causes a volume increase on the iPhone.

1. the length of the stick with tripod is 25 cm and can be extended up to 62 cm. 2. a 1/4 thread is included in the delivery.

not sure....

Ich habe es selber nie ausprobiert (ich habe den Stick nicht mehr in Betrieb). Auf der Homepage von Cygnett steht: "Trigger your shutter with the Bluetooth® remote that attaches neatly to the stick, or use it to trigger exposures remotely for photos, videos and time-lapse sequences." Das heisst, dass es gehen müsste.

In principle, yes, as long as the mobile phone has a Bluetooth connection. As far as I know, this is the case with all newer mobile phones. You can find this out in the specifications.

if the stick is displayed in bluetooth, have you also established the connection? is this also displayed in your mobile phone?

Yes it is compatible with all samsung phones (according to the manufacturer's website)

I would also be interested to know whether the holder is suitable for an IPhone 8 PLUS incl. case.

Bluetooth has a range of around 20 metres.