Main Lines
Any line 10lb to 15lb, will do. I prefer to use super-lines that are fluorocarbon coated such as Spiderwire Ultracast Fluoro-Braid, as compared to monofilament lines. This is because super-lines are pound for pound thinner in diameter compared to monofilament lines. The disadvantage is that they float and they have a high amount of drag in water. Hence why I prefer those that are Fluorocarbon coated. Fluorocarbon coated super-lines sink faster and they have less drag in the water.
Note that one will be fishing for prawns in river and rivers have currents. A low drag, small diameter line will certainly be advantageous. This means that the prawn will feel less resistance when taking the bait. Also, super-lines do not stretch and that is great. Sensitivity is certainly higher. Pressure is a lot more consistent.
Of course one can use monofilament lines too as super-lines do cost more. Monofilament lines do work but they will be larger in diameter unless one opts for lower poundage. The other thing is stretch. Monofilament lines do stretch (some more than others). A softer tip rod plus a stretchy line also is definitely a disadvantage. Maintaining pressure is harder, and setting hooks become harder too.
Leaders
As for leaders I prefer fluorocarbon lines as they are stiffer, the stretch is very low, they have less drag, and they sink faster. Fluorocarbon lines are also harder to see underwater thanks to their density. They cost more as compared to normal monofilament lines though. Normal monofilament lines can of course be used as leader lines too, just that they do not have the advantage of being almost stretch free, they do not sink as fast, and if the water is clear; can be seen by prawns. The other option are Fluorocarbon coated monofilaments. They still have stretch but they sink faster and have less drag. 6lb to10lb leaders will be good enough.