Hey, I've had the monitor for over a year now. You can connect two HDMI devices as well as two with Displayport. No problem, you don't need an adapter. You can even connect all four together, then you can split the monitor into four pictures all at once.
If by "pictures" you mean windows, yes it is possible to open 4 windows and dock them in the corners (e.g. Windows 10), BUT; due to the low resolution, each of the 4 windows will only be able to display a small amount of information in moderate resolution.
This screen with 4K resolution and Windows 10 window management is a dream for work.
All connections are on the back. Wall mounting kit is not supplied but here you can find one I used myself for the monitor and I was very satisfied.: https://www.tutti.ch/de/vi/aargau/tv-audio/fernseher/vogel-s-wall-3225-tv-wandhalterung-mit-drehfunktion/24708278
The Playstation passes the signal on to HDMI in 4K, yes. But most games are of course not rendered natively in 4K, but upscaled. The performance is simply not sufficient for 4K native.
Even a GeForce GTX 1080 for 750.- Euros can't do that.