The pros and cons of hunting RSA in January? You've heard the cons - hot, sometimes very hot, buggy, and often very humid. Another con is that the brush may be very thick - to the point where finding the animals will likely be more difficult than it is in winter, when the grass is generally lower and the leaves are off the trees and bushes. The pros? Well, there won't be much competition for the game (other than perhaps local meat hunters), and the walking will be much quieter!
And using a local taxidermy firm? The pros are the cost of the actual taxidermy, partially offset by the extra cost of shipping fully mounted trophies (they take up more space, hence larger and heavier crates). Another pro may be that your work will be done faster than if it was done in North America - but that depends on the taxidermy at each end. You may have a local taxidermy in the US who works fast; many don't.
And the cons? I've used a number of taxidermy firms in South Africa, in the Northwest Province, the Limpopo, and the Eastern Cape. Each time it was the triumph of hope ever experience. I have never found the work to be as good as the work I have had done in North America. In some cases, the work has been so bad that I've trashed the taxidermy upon arrival. I've given up and don't use local taxidermists any longer.
Understand that in South Africa, it's extremely unlikely that your work will be done by an actual taxidermist as we would think of them in North America. The work will be done by one or more local workers, who will be supervised, to a greater or lesser degree, by a taxidermist. It will come down to quality control. Every time I was promised "the work won't leave here until it's perfect." Well, every time, we clearly had different views of perfection.
Good luck with your hunt. I'm envious - I'd love to do my first hunt again!