I don't think the number of stitches on each needle matters too much at this point. I don't know what they mean by Knit alternately
but the picture does show 2x2 ribbing so that's what I do. If you want 2 knits or 2 purls together at the end of the needle, set it up that way. When you get to the heel you can make sure you have the right number of stitches where you need them for working the heel.
Since you've not done socks before you might want to watch Shandeh's tutoria
l for socks. I started with Lifestyle socks to learn how to do them (but that's toe up and your pattern is top down) and made my first pair in worsted weight yarn. As a newish knitter I found it easier to learn the steps required for socks in a heavier yarn using larger needles. You might consider a pattern for thicker yarn for a practice pair and then do the sock weight yarn.