Sys admin tasks

[xyle_one]

Not sure where if this is the right place to post as it isn't network specific, or application specific.

I have become more and more responsible for our internal network at work. This includes our linux web and email servers, our internal linux file and print servers, as well as the developers/designers workstations (mac and windows). Our office is small and no one before me has created any sort of documentation of how and why things are setup.

I am wondering how you should do this? Do you just keep a series of documents available that list whats what, and where things are, and how things are setup, and why things are setup the way they are?

I am starting to take inventory of everyones machines, disk size, space remaing, ram, same with our servers, but what else should I do? What are some best practices in doing systems administration?