What's the more appropriate word for busy-ness?
Solution 1:
workload : 1. The amount of work assigned to or expected from a worker in a specified time period
Solution 2:
In IT I've heard people use the term "utilization" where 100% utilization means that a given member of staff has absolutely no free time to take on more work. It might not be obvious what was meant by that without context though.
As mentioned elsewhere workload is probably a good choice.