Complete set up would be:
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Gas bottle - 2 or 5 kg is the norm
Gas regulator - dual gauge is the norm
Quick disconnects - 1 x grey, 1 x black for each corny
Taps - option are regular, flow control or flexi (I have flow control and there fantastic)
Beer line
Gas line
In relation to the size of the pipes, if you buy your stuff from norm on eBay then he includes all of the pipes and quick disconnects.
The other big investment is whether or not to go the kegerator route, if you do you will need to buy a fridge that is big enough to fit a couple of cornies.