I use the Swisscom Internetbox 3: The WLAN-Box 3 is a triband WLAN device and supports the new, interference-free 6GHz WLAN band according to the Wi-Fi 6E standard. The diameter of the outward-facing part is 7.5 cm and protrudes 1.5 cm. The wall thickness (wood) in my case is 7.5 cm. The peephole can be fitted to different (smaller) thicknesses using the screws supplied in different lengths. The plug-in mandrel is conical: the drill hole is 16mm on the outside and at least 13mm on the inside. The screen (mounted directly behind the camera) is connected with a short flat cable. The camera must be mounted as close as possible to the front of the person being captured. I have nevertheless moved it (and the screen) 60 cm sideways from the centre of the door onto the wall and tilted it sideways by 6 degrees using a 3D printed base (drill hole also at an angle of 6 degrees).

for wifi networks, no idea....
for the size, I'd say about 8 cm in diameter and 1/1.5 cm thick
I installed the camera at my parents' house, which is why I can't give a more precise answer about the size.
I didn't have to make any changes to the door but I did have to add a shim for the inner screen because the door wasn't thick enough.
Sincerely