Your membership will take a few hours to process by one of the lovely Admin team (orange above). When you become a CS member - there will be an ENTIRE new section to the forum called the Marketplace, there's all sort of traders from Painters, mechanics, renault service specialists, insurance companies (discount there too!) all sorts.
Fred@BTM is the man you want r.e. your exhaust, I'm not sure what the exact discount might be but usually something is afforded to members
As for other mods, have a look through the Clio Project section, there are HUNDREDS of various clios, everything from 1.2s, 1.4 (myself), 1.6, 2.0 and 3.0L clio projects. Whatever mods you want to do is up to you, lots of people will reccommend things like slightly lowering the car to improve the handling, new exhaust system etc, and there's plenty you can do without turning it into a chavbox!
The number one piece of work you can carry out on your car is a GOOD full service. It's important to note that the belt change on an RS clio is absolutely imperative and it must be done correctly by someone who KNOWS what they're doing with the F4R engine.