This could keep many SE busy for the next million years:  With mistakes made in terraforming Venus, there will likely be details that still need fixing after a million years at a billion dollars per year = 1000 trillion dollars. We likely will not start, unless we are over optimistic. We can, however, start spending the money now. We can develop the sun shades for Earth to later be towed to Venus when  Earth gets too cold. For best results the shades will allow the wave lengths best for algae photosynthesis to pass while blocking or reflecting most of the other wave lengths. We can genetically alter the algae for best performance in the Venus upper atmosphere. If the algae can fly, they will fix more carbon dioxide before they are scorched by heat and acid as they drop lower into the atmosphere of Venus.  We can plan the first human outpost in the cloud tops of Venus. We can start the development of robots that can work on the hostile surface of present day Venus. We can develop the technology to send comets from the Oort cloud to crash into Venus. We can gather more data about the Oort cloud and Venus, so we make fewer engineering errors.
My tentative plan is to build a snow fence that approximates the Artic circle of Earth, but perhaps with a circumfrence as  short as 3141 kilometers = diameter 1000 kilometers. With the pole shaded, Venus will have a polar down draft which will remain centered on the North pole as Venus is tited on it's axis less than two degrees. The algae will be carried by the upper winds and be brought to the surface near the North pole as algae charcoal, later algae humas, if the shades can cool the north pole sufficiently. The first 10,000 years the algae will not burn as it will take the algae more than 10,000 years to get the atmosphere of Venus to 1% oxygen. Venus has an enormous amount of  atmosphere. The snow fence will keep the dead algae and unused fertilizer from being pushed off the polar plateau by the South bound surface winds.
In 100,000 years the plateau will be miles higher than the rest of Venus which will help make the polar plateau cooler. We will likely need the sunshades until our sun becomes a white dwarf in 5 or 10 billion years.
At about 100,000 years, before the first rain reaches the surface, robots and/or genetically altered humans will cover the entire polar plateau with an impervious layer. The plateau will be slightly bowl shaped because the snow fence will concentrate the dust near the edge. Now the acid rain makes a sea of wet dust on the impervious layer which will prevent the acid from escaping the plateau. This period will be difficult for both gentically altered humans and robots because of the strong acid rain. It will be necessary to repeat the impervious layers to keep the acid trapped forever between the impervious layers. After 100,000 years or more, all the acid in the Venus atmosphere will be sequestered between impervious layers in the great polar plateau. Hopefully, the weight of the plateau will not cause Venusquakes. Now fresh rain will fall on the plateau and food crops can be grown. We brought lots of water to nourish the algae over the past 100,000 years. The rest of Venus is still 500 degrees c = 932 f, so we need to keep the polar down draft strong or very hot surface winds will occasionally blow into the high polar plateau, causing great misery. A mile high wall can be built of material that passes the wave lengths best for photosynthesis, if the down draft is insufficient to keep out rare North bound surface winds. The Sun is always close to the horizon at the top of the polar plateau, so some mirrors are likely necessary to allow photosynthesis on the surface during winter,
so the temperature is comfortable for naked humans, we can grow crops, because we have rain, but we are still about 1/3% oxygen and 90 plus percent carbon dioxide. 1/3% oxygen is ok as that is about the same oxygen partial pressure we have on earth if the air pressure on the Venus plateau is 66 bar instead of the present 90 bar. The genetically altered humans will need a prothesis to remove carbon dioxide from their blood as lungs cannot do that if the ambient is 90% carbon dioxide. We may need some additional alterations to tolerate 66 bar of air pressure. Venus has about the same nitrogen partial pressure as Earth.

We can do the South pole of Venus the same way, but the North pole already has a range of high mountains close to the North pole. At about 100,000 years we can decide if we want to continue the costly algae program, or wait a billion years for the plateau crops to lower the carbon dioxide to about 0.04 % The impact of comets near the Venus equator is a signifcant risk to the colonists on the plateau as a misguided comet could hit the plateau. A billion humans can live on the 800,000 square kilometer Venus polar plateau.   Neil

Fortunately the sun will not be turning into a red dwarf during our life times or even our grandchildren's lifetimes.