Question: Assuming the next step in space exploration is to make Mars habitable for many people, what are the steps you take to get there? Where do you even start?
You have
- Make funny startup company, spend all your moneys
- get the rocket
- lift enough from earth
- send it to mars, wait until arrival
- catch mars, get to mars orbit, and mars surface.
- collect enough data about mars
- test technologies for in situ production of oxygen, fuel, water, food, energy
- send equipment for energy production, hydroponics, food, peoples
- make shelter for humans
- send humans and let them assemble stuff
- begin to produce energy, enough for food, for production, for expansion.
- investigate local resources
42000 lines later
I do even know where to stat answering your question, but one you may be sure, in those 42000 lines terraforming related are 0 lines. Even profit do not contain terraforming.
Mars, beauty of cold, atmosphere less desert
I can't resist, I have to throw a couple of stones in the Idea of terraforming the Mars.
It may contain samples of microbiological live for each extinction even on Earth caused by asteroids, or just results of hitting Earth by asteroids, for last 200 millions years or more.
The research of the Mars in its current state is very interesting topic and there are a lot of questions unanswered, you may wish to look at that video The Lightning Scarred Planet, Mars
Meteorites on mars, are better preserved, and filtered by atmosphere of Mars at some parameters. We have to investigate the difference and get all data from that difference.
Scientific value of current state of Mars is very high.
Terraforming
If you asking where someone have to start in terraforming project of Mars
Answer is simple, but probably not what you are looking for: Research.
Research planet first. Before do, you have to understand it in details. It's not enough to just add atmosphere, and water. You have to be able to answer question will it trigger volcanic activity, mars-quakes. Which air flows it will be, where place water, where not, how the surface will bend under seawater pressure, which changes in relief as result it will be.
May it cause some stress on the planet surface which will cause 10-100-1000 years later flows from sea which may destroy some natural dam and lead to catastrophe with killing millions(or more) of people on the planet?
Or will it flow somewhere with big dry sediments which will react with water leading to building up stress in mars crust and lead to mars-quakes. And you better know where and why such events may happen, to prevent them.
Terraforming, biology
After you have made mars habitable for humans, it will mean Mars will be habitable for microbiological life, which is not all good for humans, not all at all.
You have to understand first how to make biospheres in general, we do not know how, at the moment. We had some attempts, of artificial setups, not all of them ended good (Biosphere 2).
Australia have problems with species (as from history Rabbits in Australia who do not have native enemies, who are aliens to native ecosystem.
Terraforming
Now what you asked for(maybe), but first I wish to point at least these articles on wikipedia Terraforming, Terraforming of Mars
After researching mars. You may wish to be able convert 25 teratonnes of CO2 to O2, also you may have to add another 2500 teratonnes (or 2000 if you produce 500 teratonnes of O2 in place on mars, from mars oxides) N2+O2 mix for 1bar pressure on mars.
So Second you have to do, is to be able move relatively big masses in space.
And with these capabilities and problems involved with mars terraforming Space_habitat's looks totally viable and very good alternative.
We need much peoples on mars to research it. The process of making it possible will improve our space capabilities, and will make other solutions possible, thinking about Mars as about second home, not wise.
Probably some day we will make planet, or will make many planets world-sized zoo , but until then we have to learn and develop our knowledge and practice.