11 March 2013 at 13:04
In order to become a tax resident of South Africa you have to meet the tests written in that blog post. However if you demonstrate that you intend moving to South Africa permanently or at least intend to make it your home for the forseeable future then you could be considered a tax resident. This is different to being a resident for passport purposes or for your work permit. If you are only going to be in South Africa for 4/5 years then you could spend much longer per year in SA, but as long as in the 6th year you are in SA for less than 91 days.
Buying property is an indicator that you will be changing your home to SA permanently which could make you a resident, so you need to make sure that if you buy a home, you still intend to go back to the USA in the next 5-10 years.
All income earned in South Africa is subject to tax regardless of whether you are a tax resident or not. However if you are a non-resident then any income outside South Africa won't be subject to tax in South Africa, but probably taxed in your case back in the USA.