what is the style of music? if classical, i'd arrange them in typical fashion seated or standing next to each other at an angle and stick with an MS, Blumlein, maybe ORTF stereo pair at a distance. that and find a proper concert hall.
if pop, i'd probably start with the same arrangement anyway, unless you want to goof with your pannings later, then you might separate them and get a little closer.
i'd also put dynamics at the bottom of your list for mic choice.
ultimately, the style of music has the greatest effect on how you choose to mic classical instruments, but I'd usually have a traditional stereo pair set up to get the ensemble as a whole, as this is what classical musicians are accustomed to. sticking them in the sound lock with headphones tends to throw them off.
