Couple of issue on:

https://docs.opsmanager.mongodb.com/current/core/requirements/

First, early in the page, I see the following statement

Ops Manager Monitoring and Automation require a server for the following components, which usually run on the same machine. The server must meet the sum of the requirements for both components

But soon after, I see:

The Ops Manager Application Database holds the monitoring information for the Ops Manager Application.

The database runs as a three-member replica set. If you cannot allocate space for three data-bearing members, the third member can be an arbiter, but keep in mind that Ops Manager uses w:2 write concern...

These two statements are at odds: you cannot run a three member replica set "on the same machine".

Other issue is that the failure to provide storage requirements for the "Ops Manager Application Hardware", and CPU requirements for the "Ops Manager Application Database Hardware". Express RAM requirements for the "Ops Manager Application Database Hardware" is also unnecessarily confusing.