1) it'd be nice to have an ap in there to avoid all of your damage being easily mitigated by one or two items. but it's not necessary, assuming your team can snowball and destroy, as an all ad team will do. i've won games where the setup was entirely ad for us. our mechanics and AA power destroyed the enemy team, which was playing standard.
2) yup. it's all about an immaculate early game and finishing quick. a friend of mine picked talon mid in draft second. this is usually a bad idea, but somehow the enemy mid went annivia and got himself hard countered. he went something like 8/0/1, and with few sources of ap damage from us, we forced a surrender at 20.