A better solution are robots, robots are way better at surviving in space than we are, they have survived in Mars for years without any supply. So a more feasible set of milestones could be:
- Engineer self-replicant robots in Earth. We are still far from doing something like that but it seems something that we should be able to achieve at some point. Seeing that we humans are able to extract energy and resources from Earth, and build robots, there's nothing indicating that robots shouldn't be able to follow the same steps once they are advanced enough.
- Modify those robots to be able to self-replicate in Mars. Seeing that current robots are already able to survive in there, they have a much better chance than we have to build a sustainable environment for themselves.
- Once robots have a self-sustainable environment for themselves, put them to burn resources to pave our way there so that once people get there they are able to survive comfortably.
Yes, people made great discoveries by sea, but people had been surviving for long periods of time on the sea, and they were great at it. The same can't be said for space in current times.