Hi Paul,
Just brought a second hand Megane RS myself, so I've done a bit of homework...
All RS has LSD except for the 2013 Megane RS Sport Edition, you can spot them by the silver Tibor wheels, dark blue paint job and the Recaro seats. They have the softer Sport suspensions as well.
According to the cost of ownership from Renault -
60k (72months) - coolant/brake fluid replacement, pollen filter, spark plugs, fuel filter & 100k (120months) - Timing belt.
From July 2014, all RS cars received 5 years warranty (if that's important to you)
Gabe