This is going to make me sound really stupid. I'm an utter newb to this stuff.

While the easiest way to do this would surely be to stump up the cash and get it done with a proper setup, I'm trying to figure out if my audio setup would work for doing a quick and dirty rehearsal-room track or two. Recorded stuff at home before, but never anything like this so any tips would be appreciated..

I've got an external soundcard that can handle 4 inputs (two RCA, one low impedance XLR and one high impedence XLR), so I'm thinking of doing two run throughs:
First run:
Single mic drums (probably gonna sound awful) through the RCA
Bass (either direct into the hi-z input or mic up the amp)
Guitar 1 (mic'ed amp)

Second run:
Vox and violin (direct input)
Midi keyboard

I guess I'm wondering if this would even work? Would all the signals bleed together? I can imagine the drums getting onto the mic'ed guitar amps. Perhaps the drums should be recorded on their own first?