This is not my expertise.
But, I can say you that, you either purchase licenses by cpu or by user count(named user plus)
I can suggest you to read ->
http://ermanarslan.blogspot.com.tr/2017/01/oda-quick-tip-for-cpu-vcpu-counts-named.htmlYou can also read more on licensing here ->
http://www.oracle.com/us/corporate/pricing/databaselicensing-070584.pdf