High load on OS X Server
That load seems quite normal to me for server. 98.53% idle CPU seems quite excellent for a light server load. There's no point in direct numerical comparison the macOS load average of the Mach Kernel with linux, AIX, BSD or other UNIX since the underlying architecture is different here.

What does translate to traditional UNIX system is counting active threads and watching overall CPU utilization. With more than a thousand threads being actively run (maybe a third are inactive enough to be marked "sleeping"), I wouldn't try to tune or change anything if I saw that on any of my hundreds of production Mac and OS X servers.

If you're really curious, I would run top -u -s 60 and let the system reach neutral (in iostat the 15m average you show is higher than the 1m average, which means the CPU usage is trending lower - when the three values are about the same, that's a good neutral to measure). Also, run sysctl hw.logicalcpu so you can normalize the value you see to the cores that are available. Even when your load is higher than the CPU available, it might not be a problem if your constraints are for IO, network or elsewhere than the CPU.

What are the top 5 CPU using processes when you have a slow refresh on top? Those will be causing the most load in your situation in all likelihood.