Perhaps the biggest problem with using an underlying figure is that you have a lot of geometry overhead that you don't need. I'm not sure just how much RAM an invisible figure uses, but the Daz unimesh is some 70,000 polygons. If you want to do the work, a standalone figure is best, I think. And there's no reason why a catsuit can't be used without any figure inside. The body parts have to have the same names for a clothing item to conform, so a pose file will work the same.