Here's the gauge: In Garter Ridge Pattern (knit all rows) with larger size needles (#5), 22 sts and 28 rows = 4".
They suggest size 5 and size 6 needles. I'm using size 4 and size 5.
That's funny you both are not going to do the ridge rows and that's one of the things I love about the design.
Over the weekend I'll post a picture of mine so far. I really am enjoying this project very much. The pattern in the back is holding my interest and I'm not bored knitting it.