If you are using a PA anyway (vocals) micing amps is nice because you can mix the sounds on your mixing console rather than fooling with amp volumes. Depending on how big your room is, you don't really need to mic the drums (they're too loud anyway). If you get into bigger situations start with kick and snare mics. The bigger the venue the more drum mics are needed. My drummer uses 7 mics, but we play a lot of different places.