2. If we assume an orbital platform is like a ring (similar to Halo), and if the diameter of this thing is 2km, then it would need to spin very fast (70m/s). This is okay, until you realize, that so much speed means a lot of difference in gravity from the floor to ceiling. For example, a man who is 2m tall, would feel 1g on his feet and about 0.95g = 9.3m/s^2 on his head. The difference in g would give rise to different health issues. You could make the station bigger, but then it would be probably better to stick to a natural body that is similar size instead
At the 1km radius you give, a 2m human would have head at 0.2% lesser acceleration than feet. Am I miscalculating? Note that 1g is just one place in the design space, though an attractive one for a big enough station.
(So what's wrong with g = v^2/r? Nothing -- both v and r change in that change to g. To first order, they cancel out in the change to v/r, leaving only a linear factor.)
Assuming 5% variation from head to toe is tolerable, a 40m radius habitat would suffice, which could be rotated at 20m/s.
There has actually been research done on how humans tolerate rotational gravity (although not long term, AFAIK.) A 30% gradient at 0.5g is reportedly "disturbing". But perhaps long term one could become acclimated, just as one does at sea.
Having lots of people with lots of babies in a floating tin can is not a problem we can easily solve with our current level of technology.
Within my lifetime, I have much more faith that we'll be able to construct habitats out of dirt on planets with an atmosphere than modules out of asteroids in the vacuum of space, and that's the appeal of planets in general, and Mars in particular.