(Re) understanding accessibility

So, the WCAG 2.0 FAQ is up. We’re currently working on redesigning our website – it’ll be quite radically different from our existing site. This is also a good opportunity to get all the accessibility features we can into the site, including all the ones we always wanted but never had.
I’m trying to get my head around all the advances in accessibility, trying to understand just where we went wrong, trying to work out where the shortcomings in Plone are. I’m also trying to be more active on the mailing lists, as some of the brightest people in accessibility seem to lurk on them.
Here’s everything that’s currently on my ‘not-sure’ list…

  1. Alternative text – just how should this work? I’m of the opinion that unless an image can be interacted with, or expresses data, it is decorative and therefore alternative text would actually be inappropriate as it would read something out of context for a screen reader. 456 Berea Street has some useful information but it’s not conclusive and by no means a W3C recommendation.
  2. Fixed size – our new design will be a fixed size design, but should we offer a non fixed style? Should the size be fixed in pixels or with font relative units?
  3. Navigation – how the hell can we maintain a sensible, logical page order while having all these wonderful new page elements?
  4. Semantically correct markup – how best to mark up elements of the page that fall outside the realm of being obvious headings?

I’m certain there will be more things that will come to mind on this. I would really like this site to be an example of absolute quality when it comes to both design, but also in terms of accessibility. What things should I be aware of?