Is the sign for 'nobody' the same as 'none'?
Yes, they are often signed the exact same way! In ASL, the context of your sentence will make it clear to the listener whether you mean 'none,' 'nothing,' or 'nobody.'
Do I absolutely have to shake my head?
Yes, shaking your head is a required non-manual marker for this sign. In ASL, negation is shown on the face and head, so the headshake is just as important as the hand movement.
Can I sign this with just one hand?
While casual or lazy signing might sometimes use one hand, the standard, most accurate, and clearest way to sign 'nobody' is by using both hands symmetrically.