Let's see if I can help you some.
1. You're right about Great Britain. As we say in our Teacher's Notes, Geography background, if you're coming from Year 3, one of the goals of this week's questions (goal #2 in the last paragraph there on page 71) is for students to review the large colonial empires of the world, and Great Britain's topped the list. Famously, as the world turned each day, "the sun never set on the British Empire"--it's territory spanned the globe.
2. Yup; France was the close second!
3. Germans (especially in Africa) or the Dutch (mostly in Asian islands) would probably be third. The goal here is to notice that these two European nations are not the ones one thinks of first as having large colonial holdings.
4 and 5: Yup and yup. You're on the right track. It's meant to be a broad question about African government: colonial imperialist holdings; they were determined by European diplomats in Europe and cut right across ethnic and political realities in Africa. Good job!
6. You're also right about who stood to gain the most: Britain. Both her position re: trade routes (esp. Suez canal) AND the natural resources (gold and arable land in South Africa) were important in modern times.
7. South America: independent nations (in contrast to Africa)! These were no longer colonies since the time of Simon Bolivar and the Monroe Doctrine, whom we studied early in Year 3.
You were doing great! These are both review questions and thinking ones: trying to get students to think concretely about the relationships that geography affected!