Sadly the last remnants of the inter-city operation was suspended in February, due to (another) fatal accident, and has not resumed yet. HOWEVER, their website is showing that they are back from 27 November 2020. Timetable details can be found on independent travel agency website
www.southafricanrailways.co.za I've used them a number of times and they were OK. Apparently no dining facilities or bedding at present due to COVID. [bring your own. You can buy a blanket and pillow quite cheaply in lower end shops such as PEP Stores].
The main line trains were pretty safe to travel on, but beware, they are not at all punctual: 10 hours late or more was not unusual. So leave plenty of time in your plans, otherwise you will be fretting and not enjoying the trip. Generally the staff are pretty helpful, as long as you pass the attitude test! seat61 has quite a bit of detail, but 'talks up' the experience into something better than it really is! It is no longer the semi-European experience it was in 1985.
The Premier Classe train (once weekly Jo'burg-Cape Town & return) is an affordable luxury option if it is running, but no more punctual.
Rorke's Drift is nearly half way between Jo'burg and Durban. The closest stop is Ladysmith, but this in the middle of the night and I would not recommend alighting there unless you have made specific arrangements to be met (and this is a big ask on someone due to the poor punctuality). If you want to ride the train down to Durban, I would recommend then hiring a car in Durban and drive back to Jo'burg via Rorke's Drift, over a couple of days.
Victoria Falls is a fantastic place to visit. Haven't been for a few years, doing an overland trip from East London to Dar Es Salaam by train and bus. (This trip is not recommended until you have some Africa experience under your belt, but then go for it!) Flying in and out is obviously the easiest way. It is/was also possible to take a bus (
www.greyhound.co.za) from Jo'burg to Bulawayo and then a train (or another bus) to the Falls. Some details on seat61 too.
You've been to SA already, so have a pretty good idea of what to expect. Sit back, relax and remember African time! If you need any more information or advice, ask away....