Cute website.
I'd like to point out that you didn't test Chrome. However, I'm pretty sure that will load okay by default, as it shares a rendering engine with Safari.
I am no HTML god, however I did learn a few tricks over the years with HTML, so I know little bit about Cascading Style Sheets. And I read the Wikipedia article, but that's a detail. So... here's what I am sure of:
CSS, unless I have misunderstood something, is very unintuitive when dealing with the vertical dimension. Horizontal placement is generally not a problem, but CSS was designed as a styling language, not for layout as much. It could be hard to impossible to implement what you're thinking about in regards to your second question. It might be possible, but don't count on it.
Also, in regards to probabilities of you needing to downgrade to a non-CSS website, I managed to procure an article for you. I don't know if you've seen this, but it might help. Reading through the earlier sections might answer your other CSS question as well.
http://www.webreference.com/authoring/style/sheets/browser_support/
And as far as preloading is concerned... um... the code looks fine... but... I might be missing something. No comment, for fear I'll mess something up.
I hope I helped in some small way.
-Albatross