For New South Wales, White (pp.369-372) tells us the following rates applied for transmission by post within the colony, for newspapers printed in the colony:
March 1828: 1d each
1835 Act: Free if posted within 7 days of publication, otherwise 1d each
1 January 1850: 1d each
22 December 1851: Free if posted within 7 days of publication, otherwise 1d each
1864 Act: 1d each
1 January 1874: Free if posted within 7 days of publication, otherwise 1d each
For the datestamps, I do not have an example of the first two.
White N3 has gaps cut into the side arcs. It has code letters A, C, E, I and S.
White N4 has a code letter H.
White N5 has a code letter N.
White N6 is inscribed NEWS-PAPER at the base. It has code numbers 1 to 4.
White N7 has a full circular border.
The circular datestamp below was issued in late 1902.
Hope this information helps