Sharepoint - What should a Site Administrator/Owner understand before being being designated as such?

Site Collection Administrator and Site Owner are really two very different roles. The SCA is more of a technical role and has the ability to dramatically change the way the whole site operates, including enabling/disabling features and so forth. The Site Owner is typically content focused and is more comparable to a Power User as they can only use the features enabled on the site by the SCA and cannot make substantial changes to site structure or behavior. Of the two, the SCA would need the all of the information you list whereas a Site Owner would only need to know about a third of it.

That said, I would strongly emphasize the requirement of truly understanding permissions and inheritance. That topic alone can cause more headaches than almost everything else combined!

I would also add:

• SharePoint Auditing as the question of Who did What and When seems to come up much more frequently than you might suspect
• Understanding the different Recycle Bins
• Basic list options like versioning, approvals, per-item visibility, basic workflows, incoming email, alerts, etc..