As a relative newbie I have 9, but that will about double and I think stay there. Soon to delve into NiMh more seriously for non-light purposes mainly, and those will number about 40.
Not yet, too low a current and capacity for the volume and cost. Something that big should have at least 10kmAhr. Just over 3 x the size of an 18650 and closer to 4 x actual interior volume but barely twice the capacity.
its my favorite small multi-cell light i use for dog walking. especially since i made carriers so it can run other cells too, including 16340, CR123, C-size, AAA size, AAAA-size, AA in various configurations, along with D-size, 14500, 18650, 17670, 26650, 32650.