I don't mean to hijack this thread, but is there any major reason to separate them? Is it just personal preference?
Whats a good size to cut off an offshoot or basal or whatever?
Looks like a basal to me. I don't separate basals until they're about 4", but I don't let them get to more than about 6" before removing them. It depends on how you slice it. If you're not good with a razor blade, your basal won't have any roots...I've never lost any though.
In my personal experience, a basal can be a bit taxing on the mother plant. Sometimes the mother plant will slow down in growth as the basal is born (and even continue this slow growth pattern as the basal becomes its own entity), so separating the two plants is often the best course of action.