Since the car is an 06, it has a 2.0 Duratec which is timing chain, not belt. The Zetec's last year was 2004.
All depends on what you want to do with the car. I would do suspension first, but motor mods like intake, exhaust, and a tune would also be nice to add. No need to do anything with motor internals unless you are adding boost (and even the FSWerks kits work fine on a stock motor).