Minimum is like 0.5 dtons per console, but then there's ergonomics issues. If you want optimum crew sanity, you give them more room....
You can have a console support more than one system, but then it's multi-tasking, and splits it's C+S over the number of tasks. So if you have a TL12 ship, and one console running Jump, Manuver, Power and Life, 4 tasks, then it's got C+S of 3 each... and only a 50/50 chance of doing even routine tasks when on its own. Not good for when the crew wants to take a nap.