Yes. Or at least have clinically isolated syndrome with optic nerve or spinal cord involvement. (Devic Syndrome-neuromyelitis optica is a demyelinating condition that can convert to MS.
Yes and no. MS is an inflamatory disease of the central nervous system. It can affect the brain and spinal cord or only one or the other. you can have lesions in the spinal cord but not the brain, although this is rare. Usually you do have some brain lesions.
Unlikely. Although unusual, sometimes MS shows up on spinal cord MRI initially, without abnormal brain MRI, but your normal films most likely represent another diagnosis.