Every time I read about colonizing another planet, I think about how we correctly don't want to colonize the bottom of the ocean or the Sahara desert because it would be completely uneconomical, and yet either would be much easier than this.
For Earthlings, the open ocean is harder to survive on long-term than deserts like the Sahara. Maybe on par with living off the land on Antarctic. Never mind all that corrosive stuff in Venus' atmosphere.
Doable in theory, yes. But HARD (and then some). That's ignoring the economics of such an enterprise.
On the upside: still easier than interstellar travel.
But potassium, sodium, calcium, magnesium, silica, iron oxides, nickel, titanium etc. are available on the surface.
> It would be akin to a city floating on Earth's open ocean. With all food, household items etc, and even construction materials produced via extraction from the surrounding ocean.
Akin in some senses, but let's not omit that another planet would be far, far more difficult. Humans do live on boats and islands in oceans; we can breathe the air, drink the water (if desalinated), eat the fish, swim, build boats from resources, etc.
And the only working ecological system we can study is being destroyed by humanity and capital on record pace.
A closed loop ecology for, say, survival on Mars, is an interesting question that somebody might need an answer to but there is no reason why it needs to look like the Earth with oceans and all and it might lean heavily on bacteria that live in vats or 24 hour illuminated agriculture or something.
Meanwhile it is not so clear that from a scientific point of view that some experiment in a greenhouse can give conclusive answers about the ecology of the Earth where so much is going on.