Planning this North Scotland trip for March, is it foolish?

Why March? I live in London and will be getting the Caledonian sleeper train up to inverness. Tickets are drastically cheaper in March than April. And im also hoping I might get to catch a glimpse of the northern lights on the orkney islands. Ive already decided to delay the trip, so I could put some extra money aside for a more expensive ticket. Maybe someone with experience of the region can give me some advice?