When it say's 'work 7 rows of the rem 210 sts' can I just confirm that means to work 7 rows of what is technically row 15 (k1, *k2tog, k25, slip 1, k1, psso, 25 sts cable patt* re from *to* end with 1.) And, does this follow suit for the other rows where it tells you to work 7 or 4 rows on the rem st?
No you don't do it on every row; the 4 rows given are for the dec rows only.
It looks like it's stockinette stitch with the cable stitch pattern, that's what you work between the dec rows. Here'a another way of looking at it -
Row1 - dec row
rows 2-14, pattern rows (stockinette and cable stitch)
Row 15, dec row
rows 16-22, pattern rows
row 23, dec row
rows 24 - 30 pattern rows
and so on...