I want to add a third and fourth options for the right sidebars, so that I can display different sidebars on different pages.

I don't use the left sidebars at all, so would be happy to use the left sidebar settings in the Admin and just update the css....I just don't know how!

If you could please offer some advice I'd be greatly appreciative!

If you want to have different widgets on different pages check out some of the plugins that control widget - widget logic is one plugins that allows you to decide which page to show the plugin on.

Ok, that sounds like a very good idea, thanks!

Even so, is there any possibility of hacking the CSS code to make the 'left' side bars float right, just out of curiosity?

if you want to hack enough, anything is possible (grin)