Short answers, pulled from the story.
The Union of South Africa existed from 1910 until it became a republic on the 31st of May 1961. This period began with the implementation of the South Africa Act 1909 and ended when the country adopted its new constitution.
Louis Botha served as the first prime minister heading a coalition representing white Afrikaner and English-speaking British diaspora communities. He led the government after the formation of the Union in 1910.
Sir George Grey's plans failed because the British Colonial Office overruled his ideas and ordered him to desist. His recall from post followed his refusal to abandon the concept despite official opposition.
Roughly 28,000 people died in concentration camps where Afrikaner civilians were interned by British forces. These deaths occurred during guerrilla operations that included scorched earth tactics against Boer holdouts.
The National Convention convened between 1908 and 1909 in Durban, Cape Town, and Bloemfontein. Delegates met behind closed doors from the 12th of October to the 5th of November 1908 in Durban before moving to other cities.
South Africa became a republic on the 31st of May 1961 following a referendum held the 5th of October 1960. The government led by the National Party withdrew from the Commonwealth of Nations after this decision.