*ignore the shakey pictures. i cannot hold my hand still.
Screw your standoffs to the board. I reccomend 5mm under the keeb and 10mm where the parts are supposed to be shown
Solder in the diodes. Make sure the black line is facing towards the square pad.
Solder the buttons and the LED, making sure the flat side of the LED matches up with the flat side of the LED footprint on the board. If you want your LED to be on while your board is on, solder a 220 ohm resistor between two pins on opposite sides of the right button, as in one leg on the right and one leg on the left side. If you don't want it to be always on, just dont press the button. Otherwise it might burn out.
Solder in the switches.
Put some electrical tape where the Pi is supposed to touch the board. There should be no electrical contacts but do that just to be sure. Hold the pi still and solder it directly to the board, if you want putting through the holes some diode legs.
Put the keycaps on your switches. Get a thin piece of acrylic and cut it to the right size, make the holes to put the screws through and screw it to the standoffs over the components in the middle.