_Red The large board seems to be mostly a breakout board with voltage regulator, usb-c port and presumably a usb communication chip to interface with the radar chip.

_Red You don't need an UK plug. It's removable, you can use a matching UK plug.

_Red Yes as long as it is 1S (one cell in series).

_Red It's a regulator. If you need to limit current, wire a high power resistor in series.

_Red No, this is a buck converter. It can't boost.

_Red It seems to be a common cathode two-color LED. You can just desolder it and extend it out with some wire, making sure the polarity is correct, or split it into two separate LEDs. To do this, connect both cathodes of the LEDs together and solder them to the middle hole. Then solder the anodes to the remaining two holes.

_Red This is a buck converter. It can only convert from a higher voltage to lower voltage. What you need is a boost converter.

_Red It's a kit. That's the point of a kit, it's sold without electronics and fully unassembled.