I think this is the wrong objective at present to self sustain in space. I'm working to try to find some alternative positive future vision.
We are nowhere near able to self sustain in Antarctica, in the Atacama desert, in Siberia, or on the top of Mount Everest. Yet all those places are far far more habitable than Mars. In terms of habitability, Mars is far more like the Moon than it is like Earth.
Indeed, for thousands of years, humans have only attempted large scale colonization of places already occupied by humans. There isn't even a huge amount of interest in colonizing the Sahara desert - we could reverse desertification there far more easily than we could colonize Mars.
So, I don't see it myself. I think we should start with the Moon. Which is also a place where we have at least some chance of economic return, of the settlement paying for itself. That could work. Settlements that are useful for Earth could be supported by humans on Earth at some ratio, say a hundred, or a thousand of us on Earth supporting each settler in space. If they are doing something of great value for Earth, or even just because they are wealthy and can afford to pay, that could work.
I think we should leave Mars well alone on the surface, because though humans couldn't be self sufficient there, they could easily mess up the scientific exploration of Mars by introducing Earth microbes. Because it is seeming more and more likely that there could be habitats for life on Mars. If so we want to see whatever life is in those habitats already,not just life introduced from Earth. It would be a tremendous anticlimax to go there and only find the life we brought ourselves, especially if we found that there was some form of life there that existed until soon after the first humans landed there. Or that was still surviving but bound to go extinct. That could happen. Mars life could be an earlier form of life for instance, made extinct by DNA on Earth. And many other possibilities. Being adapted to Mars doesn't mean it is going to be able to compete with DNA life, just depends what it is.
I think that before we can become self sufficient in space, at the least, we have to be able to build floating sea cities that are self sufficient on Earth. Those are probably orders of magnitude easier to make self sufficient. There i mean - using only sea water, our atmosphere, and a few rocks, floating on the sea and producing not only all their own food, but also their machines, and everything else they need.
That may be possible, some time. But we are nowhere near it at present.
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