I've pm'd you about avimap and passing SA Air Law when you get there.
One key thing is to make sure the club you are going to use are 'on the ball' as far as getting you in the air and your paperwork through the SA CAA. Go to the wrong club (hasn't been mentioned here yet) and spend all your 3 weeks waiting for paperwork as no preparation has been done, go to another school and you're legal in a day.
One initial question might be 'have you had an UK pilots for validations before?' - if the answer's 'no', be careful they know what to do and are prepared to fast-track you, if the answer is 'yes', ask how long the last one took the club to process. (CFS should be completely on the ball with all this, but if you approach any club that isn't used to UK visitors, make sure you ask the questions in advance).
Also, just make sure you have signed-off time in your log book on any type you intend to rent there - saves a lot of argument - SA is very 'type-conscious'!