For the projectors, check on Matrixowners.com. There are two different ones for sale. I think the entire kit goes for around $150-180. You'll need to bake your headlights and open them up. Then replace the bulb with the projectors (they just slide in the same spot as the bulb which you removed earlier). Then close them up and connect plugs here and there. Overall its pretty simple stuff, some wire-connecting and the effort of baking and resealing the headlights.
Depends on what you're looking for. A lot of good parts are on neverenoughauto.com . You can also check the matrix site for used parts that go for much better deals.
Strut bar for the front and sway bar for the rear would tighten up your handling a bit, as would installing lowering springs or, if you've got a big wallet, coilovers
I've got a set of the 15-LED dome lights from ebay. They work great so far. Just pop open the cover, remove the bulb, insert the bulb-thing of the LEDs (which are on a separate board with double sided tape on the back) and stick the LED board over it. Its a snug fit but the cover pops on again easily.