For OS 9, there are themes, which I love that they included in OS 9. http://resexcellence.com/ is a good place to find them. And also, there is Kaleidoscope, which is an extension with various OS 9 themes. You can find Kaleidoscope at:
Congrats on the buy. If I were you, I'd probably put Tiger on it alongside OS 9 so you can utilize TenFourFox as your browser. My Clamshell (see my signature) runs Tiger surprisingly well and you have almost double the RAM and a higher resolution screen.
Woah - blast from the bast, I'd forgotten all about that site.
Those Pismos are really nice I've heard, rock solid and had some nice upgrade options IIRC. I don't know about price, I haven't bought an older Mac in a long time. I remember paying $160 for a clamshell 300 MHz iBook G3 nearly 5 years ago and thought that was a good deal (Also paid $375 for an 800 MHz iBook G3 some time after), I guess prices have dropped.