Android tablets crash course

[Quinch]

So, I'm fairly new to the whole smartphone/tablet arena - while not technologically ignorant {worked the helldesk previously}, a lack of both funds and interest pretty much added up to falling grievously behind on all manners of consumer electronics. Now that I've gone into a career of selling them, that kind of ignorance is something I can ill-afford.

So, with that in mind, what aspects of Android, both as an operating system {i.e. how to use it, obvious and not-so-obvious functionalities}, and as a tool should I know as soon as possible?

Also, some more specific questions;

1. Updating android on various devices - can it always be done? Some come with one version, others with another, is it a simple matter of updating the OS to bring each of them up to speed, or are there caveats involved?
2. iWorks vs Google Docs - Apple touts having an equivalent to MS Office for free {though from what I can tell, it resembles Microsoft Works more in terms of functionality}, and while Google Docs provides the same, it requires the user to be online. Is there an offline version of it as well?
3. Are there significant functionality differences between various devices, other than simple hardware and performance quality? What are the things {useful to a newcomer, that is} that are universal across all tablets running Android?

{thanks in advance and more questions as I come up with them}