ive done s**t loads to them over the last few years and my advice is, people will tell you dont touch the engine do suspension and brakes etc. im going to be different, as much as i can understand where they are coming from ill say this...
They handle spot on out the box, the brakes are awesome out the box and the engine is great out the box, however i think on UK roads they handle well enough that the standard suspension can be kept and the brakes can also be kept. an RS Tuner remap frees it up mid range, gives you a good gain (launch control is also a cool feature) a 182 manifold gives a massive mid range gain along with a decat, cat back exhausts are only worth it if your not bothered about the noise, the standard system is fine power wise (however they rust away and fall off easily) if you really want to touch the handling then a set of nice springs from eibach or H&R or the likes make a nice difference but i wouldnt touch dampers, refresh them with new genuine items if needed.
thats my opinion and what im doing in "round 2" now ive got the phase 1 as a clean slate to start with