After registering can you still use the temporary pass to enter if you cannot receive the mailed pass?
You can still use after registering ...but only up to the expiry date of the temporary pass (so would still be valid if you register early, but don't think you could extend beyond the 30 days on grounds that you hadn't recieved the card).
But I am only a frequent visitor to South Africa (and will be there same time as you), so perhaps better information will follow from a local on possibilities to extend the temporary permit.
I guess you already have seen it, but you are aware that you can get a family wild card too, yes? This works out even better value than individual wild cards.