Thanks for answering all questions, Harrison. It was very helpful.

I don't actually know if Leopard has been released for PPC or not. Tiger was, and that would run fine on a Mac Mini.
After reading your post, I've done some checking, and it seems like one can indeed run Leopard on a G4. That's very good news, although as Stephen wrote in another thread, the difference isn't that great from Tiger.

Simple answer is no. Macs have never been very well support for gaming. You won't find that many commercial games for the Mac compared to PC. Maybe 2% of PC releases ever saw a Mac release, and even then many were things like Myst and Sim City. You can get Torrent and other P2P clients for the Mac.
Ok, good that there's a decent selection of P2P clients. I'm a little bit disappointed when it comes to games, but that's not the most important thing.

Again, nope. Mac emulation is far behind that of the PC. It has about the same level of emulation available as Linux, and shares ports of many of the same emulators such a UAE-X and MAME. Amiga emulation is no where near as good for one, being based on a version of UAE from about version 0.8. Maybe even less.
That's not good news.

Probably going up as we speak thanks to MorphOS and a new found interest in the PPC Mac Mini from the Amiga community. And make sure you look for one made before February 2006, because after this point they switched to Intel and these won't run MorphOS.
Thanks for the heads up. Agree with you regarding the prices. The interest from Amiga users will probably drive the prices up a bit.