Zig Zag Lace Beanie

[Chillin Killin]

I want to knit a hat in the round, in a design similar to this pattern: http://www.knittingonthenet.com/stitches/zigzaglace.htm

Only I want to make some changes. I would like to add some purls. Also, since I want to knit in the round, I had to change the odd rows. So, these are some changes I would like to make (which would be different from the original instructions found in the link):
Row 1 and all odd rows (WS): *k4, p; rep from *
Rows 2, 4, and 6: *k2tog, yo, k2tog, pfb; rep from *

After this is where I run into some trouble with these instructions. This is what the original instructions say to do: Rows 8, 10, and 12: *sl1, k1, psso, yo; rep from *.
A) Where would I add the purls into it? And do I "sl1" purl-wise or knit-wise? Is this decrease the part that creates the zigzag?
B) When I'm supposed to "k1", why isn't it k2tog? I know it's because then I'd be decreasing by two and not one because of the "psso", but in the rows before I had to k2tog. I am somewhat of a beginner, and I see that in the photo it works out and you can't tell the difference. My question is WHY can't you see the difference?

Hope this makes sense to other people like it does in my head hahaha, and I also hope that me being a beginner and asking all of these questions doesn't seem really dumb to you guys!

Thank you!!!

[soozeq]

You would have to start with the right number of stitches for the repeats. Then, if you add sts like with pfb that's going to throw off the repeat.

So in the even rows 2-6 you could - *p1, yo, k2tog; rep from *. to make the ribs 3 sts wide instead of 2. On even rows 8-12 it would be - sl1, k1, psso,  p1, yo; rep from *. Or you could have the purls at the end of the sequence. Then the alternate rows would be p1, k2, or k2 p1.