Not the expert, but this link has a wealth of information that may help

https://www.getmaintainx.com/l...ng-you-need-to-know/

Not sure if there are metrics about how many PM's are to be done per machine. The OEM recommendations, failure data,  operational data, cycles per year, wear items all will affect the PM amounts and frequency. You may find that the same task/PM can be used on many similar assets or in some cases it is cheaper to run to failure. Do you use condition monitoring technologies, these can replace a pm/tear down repair.

Repair vs replace with new, had a rotary valve with a motor/gbx drive with chain sprocket, customer insisted on repairing, original unit ran for 5 years trouble free, put a rebuilt unit in, it lasted 3 months. The cost of the downtime far exceeded the cost to rebuild the motor/gbx. This information was then used to establish a replacement frequency instead of a rebuild, monitor with vibration/ultrasound/motor current evaluation/oil to catch potential problems prior to the replacement date.

There are metrics that show 80% PM/PDM and the results of these tasks are "world class" organizations

https://www.plantservices.com/...-value-of-pm-and-pdm

Dave