I will add a word of caution, locally-made plastics will be scarce. You need sources of hydrogen to make plastics. Water is the onlyknown Martian source of hydrogen of any size, and this water is itself very scarce.
Using iron on Mars, how are they going to get carbon and other minerals for various alloies? Carbon can be obtained from the atmosphere. Some alloies use limestone, which may not be present on Mars. Power shouldn't be a huge problem. Massive solar farms can be built and or small modular nuclear power sources can be brought to Mars.
I'm not sure that alloys actually need limestone. Limestone is used in steel and iron plants on Earth but as a flux it does not end up in the product and there are alternative methods from producing steel that don't use it that might be more appropriate on Mars.