Welcome to the site Keano

GTi's are superb cars to drive and own, I have Eibach pro-kit springs on mine (lowered by 40mm) car handles a ton better than stanard, which was very good anyways, but now looks alot better! esp on my 18" RS-GT bbs rims

The ride quality is still very good! just a tad firmer, and very drivable on daily runs to work and occasional track days!
And as far as splitters/ body-kits go, there are loads on the market.
Just take a look on the mk5 build projects section on here and you will get an idea
