Hello,
The documentation within the Unity/Wwise integration plugin refers only to the particulars of this Unity plugin. The SDK documentation is normally installed with Wwise. The default folder is Program Files (x86)\Audiokinetic\Wwise [version]\SDK\Help. Almost all the API calls work the same in Unity than in non-Unity games.
To get you started, you should also take a look at the information available in the Resource section of this website (
https://www.audiokinetic.com/resources/).
As for the question about tracking play time to avoid overlapping sounds, this is something that you actually don't have to take care of programatically. Depending on the situation, you should be able to set that up properly in the Wwise authoring tool, without programmer support. Check the limiting options for example. Or maybe the Dynamic Sequence documentation. It really depends on what you are trying to achieve. In some specific scenarios you might need the Ak_EndOfEvent callback though.