One month of the Buhari-led administration, there is no constitutionally constituted Federal Executive Council (FEC) in place. Does it matter?

IT does not bother me. This is a matter that should be allowed to run its course. The political opposition and the legislature should weigh this to know whether it is a major concern.

Otherwise, it should be counted as one of the negatives of the new administration.

Does it violate the constitution?
Everything about government and public administration is not prescribed by the constitution. However, note that there are some legitimate expectations of government and public officials, which must be met. Otherwise, what starts out as a product laziness and administrative ineptitude, could easily become a threat. For instance, where the constitution specifies that some public agencies must be set up, any undue delay in setting up those agencies might lead to a concentration of power and discretion in the president’s office.

The delay would have ripple effects throughout the system. We are seeing one major effect right now: the apparent inability to take the necessary measures to stop the rapid decline in the value of Naira.
Civil servants are currently in charge of running some of these activities, but how effective could they be in translating the President’s campaign promises into positive results?

Civil servants will always be in charge of actually running the activities of the government. An effective leader will finds ways to inspire and motivate them, to give their best service to the country, and its people.