G4 450 and cubase VST 5.0 Options

I've just bought a used Mac G4 with a 450 MP and 20GB Hard drive. I've also got cubase VST 5.0 and Logic. I'm completely new to making music, and wanted to know if my mac is going to be powerful/big enough for the job. Any advice on requirements and or the best plug-ins for beginners would be appreciated.

I'm a DJ, and want to start making my own tracks basically. I want to be able to connect my decks and minidisc and amp directly up to my mac and play samples/breaks/loops directly into the mac. This possible? Would I need any special equipment?

Cheers
ap