Whatever you do or don't do, go here, at least twice:
http://www.tripadvisor.com/Restaurant_Review-g54645-d514770-Reviews-Alpine_Inn-Hill_City_South_Dakota.htmlSome of the good ones:
http://www.motorcycleroads.us/regions/sd_black.htmlSomething not highlighted, US16 from Custer to Newcastle WY is right decent.
You can pretty easily spend the week in the Hills area, especially with a couple of day trips(Badlands and Devils Tower), save the Rockies for another time, when you have the time to properly enjoy them.
BTW, hit Wall Drug while you are out in the Badlands. This tourist trap is an institution. Way cool, for a tourist trap.
Where ya staying?