Help with adapting a stitch pattern

[cookworm]

I'd like to adapt the stitch pattern that was used for this hat to maybe a shawl, but I was wondering, in multiples of what would I need to use to calculate the cast on number?

I don't know how to calculate the multiple of stitches (for example, the feather and fan stitch pattern is worked over a multiple of 18 stitches).

Here's the pattern:
Row 1: k1* yfwd, k2tog, repeat from * to end.
Row 2: knit.
Row 3: *sl 1, k1, psso, yfwd, rep from * to last stitch, k1.
Row 4: knit.

One other thing--is it possible to adapt this stitch pattern for a triangular shawl? Would I just need to do my increases using the multiple for each row? Say for example the multiple is 3--then I'd need to increase 3 stitches each row?