When I plug my Bump Normal to Diffuse Normal my material turns completely black. What should I add &/or change?
You need to feed the bump data (in your case the Grain pattern fed through the Color Ramp to the Multiply) into the Height socket of the Bump node, not the Normal. In your current setup, the Multiply will be producing a scalar vaue rather than the vector that is required - resulting in effectively no surface normal. You should generally ensure you're connecting like for like when connecting sockets.