Is Zambia very similar to South Africa?

No, South Africa has more developed economic infrastructure that is on par with many 'emerging market' economies such as Brazil and Eastern European countries. The market capitalization of the Johannesburg Stock Exchange is more than 10 times the market cap off all other exchanges in Africa put together.
While Zambia has a high GDP growth rate, it's at least 50 years behind South Africa. Still, it may be easier to find unexploited opportunities in the relatively unexplored Zambian economy than the South African economy. Suffice to say South Africa has more areas with higher standards of living that are directly comparable to western countries.