Mars for the Many released an article about the tips of things humans would need to sustain life on Mars. The focus was more focused on the farming aspect and how to maintain farming or growing food in any capacity. Being able to colonize another planet would be a major milestone.
Colonizing anothe planet could be accomplished in our lifetime. They could develope the companies independently like the space station and send them to Mars. The only hard part would be getting the individual parts to the same area and undamaged. If they can send unmanned robots to Mars we are already in that mindset. They (and by they I am thinking like NASA or space x) could send the modules months or even years before human arrive. If they could somehow find away to recycle the salt water or make fresh water and store it, that would be huge first step.
Trying to colonize another planet does bring up a few concerns. The concerns would be that we have not come far enough or learned enough from the Biosphere 2 project. Many of the problems that Biosphere 2 had should have been resolved by now and could be applied to future plans. It was a good first step but it may have been to big of a step. Maybe if they scaled it back they may have had a more realistic view of how to maintain life.
I think if they wanted to seriously consider the same approach the do not need several biomes in oder to sustain life. The biggest hurdles would be to develope a renewable source of food. Eventually, adding in renewable sources of protein.