re: Create a self-regulating troposphere on Venus
To make the temperature self-regulating, I think we need a layer of atmosphere where water is always either liquid or vapor, and an upper atmosphere where water will always freeze. Then if the surface is too hot, water will evaporate, and convection will carry it to the upper atmosphere where it will radiate into space, cool, and form clouds to block sunlight from further increasing the surface temperature.
If the surface is too cold, then we need the planet's emissivity to decrease, to aborb more heat from sunlight. Clouds should disappear, and even if ice forms on the surface, the heat will be reflected back though and be absorbed by the CO2 atmosphere, increasing it's temperature.
It would be tricky to strike a balance, that's for sure.