Hi Tsun,
Try Avcom.co.za rather than here. There are many more people on that site who know about SA flight schools. In fact if you browse the site you will find similar threads on the best flight schools to go for.
As for the weather, around Johannesburg in summer the flying is good in the morning and thunderstorms in the afternoon (very approximately). In the Cape Town or south coast area it is pretty good all summer, with flying possible most days.
Best of luck