First, Solder LEDs in line, measure the hole needed for the LEDs and Cut that out. Then Cut the Hole for the switch.
Connect all the wires, because the powerline adapter is only 9v no further regulation is needed, fix everything with hotglue (except the 9V Battery, use Bluetac or similar for that). Top the LEDs off with the Plexiglas.
Keep in mind, LEDs get hot. So use the enclosure open, when in longer use. When first powered, turn the Booster low and slowly turn higher until it is bright enough. Mine started to flash when the power was to high.