You will need the full exhaust system I would of thought for best gains.

Maybe a remap? You will definitely need a remap to get the figures you want mate. In a perfect world the best way to do it is to get all the parts, fit them and have a live map/custom map done by the likes of MSD/Jam Sport/DreamScience. But the ODB port tuning seems to work fine and plenty of people rate it my self included.

Down pipe tbh I would get a garage to do it but thats me as i don't have the tools or patience.
Also get a set of new bolts for the pipe as well for when you get it fitted.

As yours is a 60 plate I would of thought the clutch would be ok. Mine is an 06 and the clutch shit its pants after my Dreamscience Race+ map so had the RS clutch kit fitted and been fine since. I rang DS and they said it only seems to be cars built during a certain period, earlier and later ones have been ok with 300 ish bhp. Only way to find out is to do it, just have some money for a clutch in case pal.