Right, everybody wants their car to be the fastest, coolest, etc. Probably best getting a mod to change the name of this thread to "Monaco 172 track car" or something as calling it the Ultimate clio has got you a little stick lol
My advice is to strip everything you possiablely can out of it, so you'll be maximizing the BHP/ton of the standard engine.
Get a decent set of coilovers and possibalely a whiteline rear anti roll bar.
Get the suspension properly set up for track at a professional garage.
Get a decent quality exhaust like a Yozza or K-tec it will add to the weight loss too.
Then get a year's worth of track days, learn how to drive your car on track. Perhaps to a air field track day first and push your car beond its limits so you know where they are.
Then after you've done all that then do you engine mods and get a LSD as with anything over 200bhp IMO is the limit to been able to throw it around and stamp on the loud peddle.
Have a look at the big project theads and see what gear people go for and you will soon realise what stuff is poo and what stuff is worth buying to make your 172 into the ULTIMATE clio