I bought the kicker bars for my 1500 for one, because the looked cool... and two, when you're spending that much on a lift $90 for a little extra rigidity is not much to pay. I'd say go for it.
Contact the guys at Bully's Performance for the lift and Bilsteins. They'll hook you up with the best pricing. Just mention that you're a forum member and everything that you're looking for and they'll set you up a custom cart on their website. Contact Eric or Jeremiah at email@example.com
As far as installing the Bilsteins yourself, it isn't really worth it as they would just need to come back out again. You would save a little bit of money by swapping over the hardware onto them but that's really only 20 minutes worth of work in the shop.