Hi Mike
September is spring time in South Africa so it won't be hugely hot - a typical temperature might be around 15 degrees Celsius. So I would take a mixture of shorts, light trousers and maybe something warmer too. Long sleeved tops might be a good bet but again, I would take a mixture so you can decide once you know what the weather is like each day. A good insect repellent should be enough to save you from any nasty bites. There's no need to dress up in the evenings - it's all very informal.
I've had a look through your itinerary and because you will be making quite a few overnight stays, washing clothes might be difficult. Your best bet looks like the Thanda Nani Lodge at Kruger National Park, who offer laundry facilities, according to their website. You will stay there about halfway through your holiday, so the timing is good for refreshing your wardrobe. Please bear in mind it isn't 100% certain that you will be staying at this property as it will depend on availability. But fingers crossed, any alternative lodge will offer similar facilities.
Kind regards,
Olly, your editor