We recently moved into a house with a prepaid meter - also our first experience. I just buy electricity through my banking app (Absa). I suspect most banking apps have that facility. You get a token / code issued after the purchase, which you just punch into the meter installed in your house. It really is as easy as that.
Regarding the tariff blocks, I just buy as much electricity as I can early in the month. The first 2x R1000 purchases are at the cheaper tariff, after which it gets quite expensive. I usually get around 450 units for a R1000, but any subsequent purchases drop to about 370 units for a R1000. I’ve never needed to purchase more than that, so don’t know what the next block increase would be in my scenario. My “bill” averages around R2200-R2500 per month.
We’re a household of 3 adults and 1 toddler with a domestic coming in once a week, a gardener once every second week and my parents staying over on most weekends. My wife and I also work from home permanently, so we have 2x laptops and 4x monitors running 24/7 (we never switch them off). Other than that usual household usage, including 1-2 TVs running every so often during the day and some downlights on almost permanently during the day (as that part of the house gets very little sun and natural light). So maybe use that info to judge how much prepaid will end up costing you?