I have Apple’s 30″ and 23″ as asetup, I put a stand under my 23″ so the tops line up. This is really a personal thing.
You will probably pay more for a monitor that rotates, I had a b&w Radius monitor years ago (MacII ci days) and love it for desktop publishing.
One thing to watch out for is lower priced monitors don’t have the pixel count so things are really big on screen. You will notice that a Samsung 22″ and 20″ widescreen with have the same resolution so you get no more image on the 22″ everything is just bigger. (BTW – the 20″ is $299 at Sam’s and is a great monitor for the price, I believe it has both DVI and VGA inputs also)
but as for setting them up there is nothing to it as long as your video card supports to and other than other iMac and minis there have been for years starting with G3’s.