No phantom power needed. auto gain always off. always use L gain on side unless you're recording someone playin' acoustic, even still i've hardly every switched the gain to anything other than low.
as to the level... you just need to monitor it. i think i've been known to drop down anywhere from 40-70 depending on the feed level. it's kind of tricky to figure out until the band is actually playing. better to keep it at a safe level. i wouldn't leave it at 0.