recommend getting the wheel set sorted out first. you bought a Nashbar single speed kit, is this a pair of spacers that fit on a cassette rear hub? If it is, then you need to make sure you get a cassette style rear hub, and not a freewheel type (more research homework). The cog spacing that the kit will give you will determine the spindle length of the BB you need to get. Pray that someone reading this thread has done this and know the right measurements.

BB: a Shimano UN53 is pretty sweet for the money. special tool is required to install, hope for local help.

PM me if you need a BMX cog 15T or 16T