> the "simple" task of terraforming Venus is

To drag several cubic km of metallic asteroids to Venus orbit, heat up chunks with concentrated sunlight, and roll it into thin sheet metal. Then use it as a sunshade to block out the Sun from the whole planet.

On a time scale of 40 years the atmosphere will cool down. It takes so long because not only is the atmosphere much more massive than Earth's, but the surface rock layer just below the gas is also at the same temperature, and has to lose heat too.

The high ground on Venus will preferentially be cooler and lower pressure, so that's where you can start doing stuff.