[credit_guy]

Just for a sense of scale, the venusian atmosphere has a mass of about half a billion GigaTons, 97% of which is CO2. Here on Earth, with all our industrial infrastructure, the substances we produce the most (iron and concrete) are in the low single digits GigaTons per year. The next ones (fertilizers and plastics) are in the hundreds of megatons per year. If you want to make a difference on Venus, you'd need to make millions of time more diamonds each year in some balloons in the skies than we make iron here on Earth.

[pencilguin]

It is a matter of how big a hurry you are in.

But, yes, it would be pointless to try terraforming Venus without von Neumann machines, and then it would end up thick with those, instead.

The Kuiper Belt offers more than the inner planets, provided energy is solved e.g. via aneutronic fusion.

[credit_guy]

> provided energy is solved e.g. via aneutronic fusion

You can use regular fission as a dense energy source. If you are worried about the waste, you can just blow it up. In space there's no fallout. The particles from the explosion will just move radially forever. Most of them (99.9999..%, too many nines to count) will keep moving for billions of years through empty space without encountering anything. Oh, and as a curiosity, if you blow up a nuke in space, there's no fireball. The fireball we see in movies of nuke detonations are due to the air absorbing the X-rays from the nuke and becoming overheated plasma. But there's no air in space, so a nuke explosion is invisible and silent.

[pencilguin]

Fission is not a good energy solution for the outer solar system (except maybe on Titan) because of the need for a detour through a clunky heat engine. Likewise, hot-neutron fusion.

Layered mirrors concentrating monochromatic solar irradiation into laser cavities, and beaming power to where needed, is the fallback until aneutronic fusion works.