NuVinci installation on a Micargi cruiser
Step five - if your bike already has mounts for either disc-brakes or caliper-brakes, then you'll still be able to use them (the Nuvinci comes with a standard six-hole disc brake adapter, and of course caliper brakes don't care what type of hub you are using). If you have a cheap-o Micargi like mine, and you don't have either disc-brake mounts or caliper-brake mounts on your frame - then buy a roller-brake. These come in two levels from Shimano: the BR-IM41-R and the BR-IM70-R. The 70-R has bigger cooling fins and supposedly better stopping power, although it is about twice as expensive as the 41-R. Roller-brakes seem to be the bastard step-children of the brake world (no one talks about them), but I've found the 70-R to work really well. I have it connected using a dual brake lever, along with a mechanical (not hydraulic!) disc brake on the front wheel. Look at the pictures - note that this roller-brake is actually built by Shimano for their "Nexus" internal-geared hubs, but it fits perfectly on the left-side splines of the Nuvinci hub.
What a great idea they had, to make this hub compatible with just about every style of rear brake possible (except coaster of course).