There is no minimum for cockpit instrumentation, as spacecraft can be completely automated and/or controlled from the ground.
For practical purposes, the minimum craft controls would be:
- a translational and rotational controller; in theory, these could be combined.
- a fuel gage
- a two-way radio
- life support controls
- Flow Rate (either a dial or an on/off switch)
- oxygen fraction
- oxygen level monitor
- carbon dioxide level monitor
These are based upon the combined controls for the NASA MMU and the NASA EVA suit.
A practical spacecraft should also have:
- attitude indicator
- additional internal environmental controls
- radio controls
- antenna pointing controls
- computer interface for guidance controls
- drive condition monitors
- power system monitors and controls
- door status monitors
- other mission equipment monitors.
- fuel condition and quantity monitors
Most of the controls will be multiple devices, and many will have redundancies, so each redundant system will have its own controls.
It's worth noting that the Shuttle could have been controlled with far fewer manual controls, but that the NASA felt it important to retain manual controls rather than computerized ones.
Also, the Shuttle, since it flies in US airspace, also has full aircraft instrumentation, including
- landing gear operation
- landing gear status
- flight control surface status
- control hydraulic pressures
- Approach slope indicator
- turn and bank indicator.