Ah yes, the "holy grail" of a single number that tells you everything you need to know.....doesn't exist. You can certainly do it, but most often it needs to be "unraveled" in order for anyone to make sense of it.
I produce monthly metrics for my department - how many? Try 15. A lot, yes, but I categorize them into logical sets (Productivity, Quality, Incoming Volume, Turnaround Time, etc.).
What you should do is create a trend plot (managers love pictures) of the key items, with maybe a small table underneath it so that you can see the daily numbers and how they change over time.
Specifically with your data, I would focus on comparing report % completion rate to the % available staff, and also plot trends of the actuals vs the expected standards, especially the 6.4 reports per staff, which seems to be the key productivity metric.