Does NAV provides enough capabilities to measure the available and used capacity across a work center or machine center?

Can i record the number of staff working at a particular WC/MC? How does the Capacity field in the scheduling tab of WC/MC card work?

Is it possible to shuffle resources or move capacities across WC/MC at run time?

Ultimately it depends upon how you structure your setup, but yes you can measure capacity. Staff could be a WC/MC so it depends where you capacity constraint is, machine or person, or arguably both which affects your setup and structure. The capacity can again reflect the number of resources or people within the WC, therefore if it is a manual job and you set this to 3 and you have defined it takes 60 minutes the scheule plans for 20 as you have 3 resources working on it.

Not really possible to shuffle resources at run time if by that you mean when you release prodcution, you can alter the concurrent capacities on the works order routing, which itself comes from the routing and the work centre, but it maybe you alter the work centre and reschedule to get a better reflective plan.