You cannot connect the Dell D3100 directly with a USB-C cable as it has a USB-B port. However, to connect USB-C devices, you can use a USB-C to USB-A adapter to connect USB-C devices, but the dock itself is not USB-C powered. A suitable cable would be a USB-C to USB-A adapter to connect USB-C devices to the USB-A ports of the dock.
According to our supplier :
The dock provides USB charging to peripherals, but does not charge your laptop.
This device does not provide power to the system. You will need an AC adapter that is connected to both the system and the dock for normal operation.
I have used it with an Asus laptop, an HP laptop and a Dell laptop. All no problem. Just plug and unplug the USB 3 cable. Using 2 x 23 "Full HD screens and no performance issues. No experience with 3 screens or with Mac Mini.
Which power supply unit do you mean exactly? The docking station has its own power supply unit, so the laptop must still be powered by the power supply unit supplied.
In principle, yes. I have also used it with a Surface Pro 4. If different computers (not only Surface) are to be used alternately at the workplace, this is certainly an option. If only one Surface is to be connected, I would recommend the Surface Dock.
Since I am not technically proficient in MacOS: Hardware-wise: YES - Software-wise: I don't know. In principle, it works with most notebooks that have a USB3.0 output and can use its full bandwidth; and the internal graphics must of course be able to handle it (number of monitors; intended resolutions and finally the application(s) you want to run...).