[Taz-in-Space]

Ther next question is, is 60-70 ppl too large a group for such a primitive, hand-to-mouth economy?

As a single constantly-together group?
Probably, however not all primative societys were grouped that way.
I remember reading about a nomadic society that had small 'tribes' that met other tribes once a year. At this mass meeting, the leaders of the tribes would collectively decide issues between the tribes.
With this system several hundred people could theorically be supported.