If you're looking for the equivalent of OWASP for network security then I'd suggest that testing methodologies like OSSTMM or PTES (although PTES is still rather incomplete), are a good place to look for information.
However as you say both of those will have a very large amount of information in them. This is really because network security is a less well-defined proposition when compared to web application security. It spans a wide range of topics (Unix OS security, Windows OS security, network devices, databases etc) so the range of checks needed to complete a thorough review is going to be a lot wider that it will for a single web application.
That said if you're looking for a basic set of checks for network security I'd recommend.
- Port scanning of all hosts in the target networks to establish what services they offer
- Vulnerability scanning of the open ports using a tool like Nessus or OpenVAS. Vulnerability scanners have a huge number of pre-programmed checks for common security issues so they're a good way to identify basic issues. Also if you provide credentials for them to authenticate to your servers they can do a more thorough job of checking things like patch levels
- In addition to this I'd recommend checking all management interfaces for default credentials. This is a very common issue and one that is the cause of a lot of breaches. Doing this can be as simple as connecting to each one and trying common default combinations (e.g. admin/admin). You can also review documentation for the system under review to see if it mentions default accounts (they often do)
Whilst doing this won't find all the issues in a network, it's a good first step and if you can resolve all the issues raised from this sort of scan your network would be heading in the right direction from a security standpoint.