I'm a little late here, so only a few comments:

empeg install is NO problem, if you put it in the upper slot. I don't know, if the lower one is full DIN-size. Just put an amp under the passenger-seat. The battery is just in front under the passengers feet.

If you buy the Factory speaker upgrade, you'll need a seperate crossover, cause it's normally in the factory head-unit.

You DON'T NEED a tuning-chip to power the empeg, but be prepared for jokes of all kinds...

You can get rid of the side-wind problem by mounting wider wheels.

You'll get used to the gearbox after a couple of days.

You can go on the motorway, if you don't care to be one of the slower cars.

And thanks Mark for linking the photo...

P.S.: most of the girls just love smarts...