One staff or 4?

[Ian Turner]

I'm setting a choral piece in SATB. I've got a movement here which is
always in unison, but where different parts sing at a time. For example,
it might be all four parts singing, just the sopranos and the tenors, just
the altos and the basses, etc.

What do you guys think? Should I do this all on one staff, which merely
changes meaning, or should I do it as four staffs?

Also, if I go with the former, is there a way to make lilypond's midi
output include the men's voices, an octave lower?

Thanks,

Ian Turner