Seems to me that having a transfer switch feed a subpanel with only certain
circuits on it is far too limiting. And one of those panels where
individual circuits can be flipped one way or the other is a neat idea but
again it's limiting. I think it's preferrable just to have a big switch
that cuts the whole house over so *everything* is live. Obviously that
doesn't mean you have the power to run everything at once but how much
easier not to have to run extension cords because only certain outlets are
hot. And of course the matter of hard wired fixtures and devices. Sure,
you'd have your furnace powered but what about the lights in the bathroom?
Energize the whole house and just take care on what's on at the same time.