I wouldn't say it is impossible, just impractical. Vacuum insulation might work better, if we can produce large blocks of silica aerogel it might not require as ridiculous amounts of power. Pyrogel is a practical insulator because is flexible.
I'm not so sure about the fans though...
Putting balloons below the structures would make things unstable. To make it stable you'd have to add more weight. The center of gravity needs to be below the center of buoyancy or it'll flip. To get any significant lift from an increased temperature you'd have to go pretty deep. Deeper does means denser though. I guess you could make something like a spar buoy though, but I'd need to be HUGE, like kilometers long.
>> lifting gas
Again, the thing that makes venusian colonies so cool is that plain ol' air is a lifting gas on venus. Venus' atmosphere is primarily composed of CO2, which is denser than air.
Pressure and gravity are similar to Earth, atmosphere stops the radiation, solar intensity twice that of Earth.
>> farmland
You can mine resources from the air on Venus and make more farmland. The atmosphere contains carbon, hydrogen, oxygen, nitrogen, sulfur, and a bit of fluorine and chlorine. From this we can make plastics, carbon fiber, breathable air, carbon nanotubes for conductors which allows us to make more settlements. And again, air is a lifting gas on Venus, a suffiently large plastic bubble full of air will float on Venus.
Processing air is a lot easier than processing rock. Grinding up regolith to get water is a lot harder than condensing it from the atmosphere. Granular materials are hard to work with. No such scaling laws exist for them and we can't simulate them accurately
The truth is we have yet to come up with a reason for space colonies. There are no resources out there we can't get on Earth.
This is is not supposed to be a thread about colonizing venus, it's about dying on venus.