<p>I'm designing  my website and was curious, before I go rip someone else's ideas, what were the salient considerations and questions one should ask in designing a database?</p>

I think the most important question is, "Why are you doing it (the CMS, not the web site)?"  This is very well-trod ground.  Unless you have some really innovative ideas and unique insights into how you want it to be done ... and your question suggests that you probably don't ... you would probably be better-served by choosing an existing solution.