I personally find audiosuite/offline processing a bit clumsy for most processing, because of how the preview sounds (looping and fast with short regions) and because it's not automatable. I occasionally use offline processing when I'm only going to do only one small fix and not multiple at the same time e.g. one eq cut.
I work nondestructively and render whenever I reach a certain "goal" with the sound. In terms of layering, I don't find it difficult to sum the layers either, as soon as they are close enough finished. I might "save as" to a new version number if I'm bouncing a lot of stuff, so in case something needs to be changed, I can go to a previos save and retrieve the original tracks.