[throwaway12357]

I think it's a mistake to attempt a "naked" human settlement. You should start with a robot settlement.

That means sending robots that can set the basic infrastructure (extract water, fuel, set up hydroponic farms, 3D printing, etc) for humans to live there. This will give you a considerable safety net to succeed.

One thing that echoes my mind -- not for today but in 20-100 years from now -- is the question of Mars land ownership. And how likely will cessation occur.