With regards to the power, fitting 18" wheels will reduce power transferred to the rd, unless you put a lower ratio gearbox on it. I put 18s on my 1.6, and it really sapped the power big time, but also made the brakes feel like crap, I've now upgraded to 300mm discs and mondeo mk3 calipers. No matter what you do with a 1.4, you are never going to set the rd alight unless you go drastic with either forced induction, or nitrous. You can gain a few horses with manifold and exhaust, and induction, but for how much it would cost, it's really bad bhp per £! If you know your way around an engine, you can swap he bottom end to a 1.6, that will increase your compression ratio, and the cylinder capacity, & net you around 25-30bhp. You'll need to take it easy for the 1st few miles though while the ECU adapts to the engine. And high octane fuel is reccomended. It's just a suggestion though, might be a bit heavy.