Hello, first post so..
I believe its very important to have an extensive knowledgebase for many reasons, the main oone being it can drastically cut down on your support time/costs.
Choose topics that pertain to your host and define then as accuratley as possible in laymans terms. If you dont offer a certain addon or piece of software, dont put anything about it in your KB, it will only distract the client and cause them possibly open a support ticket or chat, defeating the basis of the KB.
The more "relevant" items in your KB the better, it gives the impression you know your business and it gives the client a feeling of ease knowing they can find information about a problem at the click of a button.
And if you do get a ticket or a chat about something that isnt in the KB, then when the ticket is done or chat is closed, add the concern to the KB, that probably want the only person wondering the same thing, but since they didnt see the info, the just moved along, thus possibly losing a new sale
With that said, feel free to utilize our KB
http://mtech-hosting.com/billing/knowledgebase.php
It is in no way complete, but could be a decent starting point for you or others.