Deano,
You will have 2 sensors, one front left, one rear right if memory serves.
As for the discs, if they have any groove or dig/gouge marks, you have to replace them.
They also have a minimum thickness safetly line on them (the discs) that wears down as you use them, if it is on the limit or past the limit, you should replace them.
WHat I would recommend is to take them past any machine shop (Dave from CBF in randburg will do this for you for a couple of bucks) and just lightly skim them if they are otherwise fine, they will also tell you if you need to replace them.
I would also recommend changing your brake fluid, as this is a regular maintanance item as well, and is just as important as your pads, although you may battle without a pressure bleeder.
Why not give dave from cbf a call and ask him for a quote, you will be surprised, he is in randburg
There is also Norbrake out germiston/boksburg side.