Btw, if you get the digi 001 package, you wont need another soundcard, cause it is one.
With pre-amp, I mean a mic/line pre-amp. So you can also record vocals or mic up your amp. And if the pre-amp has an instrument input, you could just plug in directly, and use AmpFarm to get your guitarsound.(is basically the software version of the line6 POD)
You say you get monitors with the G4? Hmm, I bet those are just computer speakers, wish I wouldn't use for monitoring recordings really. I have no clue about monitors though, so I can't recommend you anything in that department.