This model is a cable chain. It is open to allow to easily change the cables inside and cable ties can be used to maintain the cable.
The file "cable chain" should be printed as many times as you need (one link for every 16mm of cable) while the other files are all used to attach the extremities of the chain to you device. The "motor" and "fan" files are designed to be attached to a Nema 17 motor and a 4cm fan. All other attaches have a 5mm hole and are intended to be screwed on a 2020 aluminum profile.
All models can be printed without support. However the bottom part of the pins in the links should be cleaned with a cutter or use a file to make sure the parts rotate easily.
The parts are designed with a 0.3mm clearance and rescaling the files will not change anything so try decreasing your extrusion coefficient if your prints are too tight.