Use between 10% and 20% infill and a layer height of 0.3mm. Having 2 or 3 shells gives it the right amount of strength. 

insert the connector into the designated space and solder the wires with the white connector that you received in the kit. 

leave the earth green wire unconnected

Insert the connector through the hole and fasten in the nut into position

For this step you will need another soldering station. Sorry for this. I think this is also specified on the  seller's page when you buy the kit. Solder the wires as you see in the diagram:

Place the cover into position securing it with some 6x2.5mm screws as in the image. Place the washer and the nut of the rotary encoder and finally, place the knob.