like shawntp said, its really up to experimentation. just try it out with both setups (although i also agree that studio volume doesnt translate that well in a live PA setup) and see which one u like better. i would assume it shouldnt be a problem unless ur computer cant handle a 45 minute set without any hickups (ex: freeze, lag, etc.).
just go try it out and tell us the results -_-.
another thing is if u decide to have drums, bass, guitar, and vocals, ur already at 4 mics minimum and that would be a pretty raw input, especially for the drums. might need to invest in a mixer w/ at least 2+2 sub outs and 4 direct outs (3 direct outs for each mic on vocals, guitar, and bass, then the alt3/4 for ur drums). its definately doable if ur computer can handle it ! -_-