I just recently made a purchase, too, and the big thing I found in my research was to go ahead and spring for the dual-body regulator right away. It's much cheaper to get it as part of your initial kit than to add it on later. Manifolds and splitters aren't too bad to add on down the road, so leave those out before you leave out the dual body option. (Of course, go ahead and get both if the money isn't a problem.) But you WILL want the ability to operate at two different pressures.
And since you're buying from KC, get the 10 lb co2 tank. They have it on sale right now for only $15 more than a 5 lb, and fills will cost you about the same. That's a lot of added convenience and savings over the long run for a small initial outlay. (Unless of course you have serious space constraints that necessitate the smaller tank.)