Welcome aboard, and the KK BabyBass is a good choice ... I use mine extensively, especially in the smaller venues.
Choosing alternative strings for DB and similar is a horribly expensive thing to experiment with. In your position, I'd just phone Kris and ask for his opinion. He's a really nice guy and very helpful, plus he knows exactly which strings work best with his own basses.
As for the preamp, it really depends on whether you'll be playing through your own backline, or going through the house PA (or, of course) both at once. In most situations I find it best to have a preamp with me, but not one designed for DB like a PlatPro.
I've had the best results with an MXR M81, standard pedal size (i.e. small) but very versatile and with the functions/features you're actually likely to need when playing a KK live. A decent alternative is the Hartke Bass Attack, but I'd steer clear of the Sansamp range for this particular application.