I'm a fan of dumping massive amounts of hydrogen sulfide onto mars to begin shifting the SO2 into water and sulfur. It's be a start in getting water on Venus. Once you have enough water, you could then begin mass injections of algae and other forms of life to slowly convert the CO2 into Oxygen. Granted if we were…

I feel like I'm the only one who got your manga reference.
JOHJ!
In the future though… let's NOT send cockroaches…