question 1: In there early days of the Dutch colony, that particular area happened to be thinly populated (if at all) and there were few conflicts with indigenous people for the first half century. The Dutch also bought some land off the tribes. Later conflicts of the Dutch were against tribes that did not possess the strength to endanger the colonists (San, etc.).

question 2: There are few areas in Africa and Southern Asia that are suitable for Europeans in terms of climate, etc. That's why you find European settlements in more "benign" climates, like North and non-tropical South America, Australia, New Zealand, etc.

Coastal South Africa has a suitable climate, and offered prospects for European-style agriculture. If you go further north, into areas beyond Rhodesia, etc., you get into climates that are less suitable for European settlements.

[note: comments about Africa, Asia, and the tropics are meant in general; there are always coastal areas that have a better climate than other parts, even in the tropics; but such small pockets are suitable only for trading posts, not for large-scale agriculture and settlements]