So, I have made some progress since Wenesday. I've also been comparing the directions in Knitting workshop to the ones in Knitting Without Tears. (Gerry I know you don't have KW, so you might be interested in this). KWT's directions give straight forward stitch and ridge counts, in KW it says that when making the first front panel (where you are making space for the arm holes) you should knit twice as many ridges as there are stitches in that section (which is 1/8 the total sts). So by those directions my arm holes should be 40 ridges high. Since I had been calculating the arm hole height as a ratio of the total it would have caused me to start them at a very different point. I like the KW directions better (seems to make more sense in retaining the jacket's proportions), and so I think I am ready to start the openings now.
As for my yarn scare, I dramatically under-estimated the amount of yarn that would be sucked up by garter stitch. And realized on Friday that I was definitly going to need more yarn. The store where I had originally purchased the yarn had no more of that particular colour. So icalled around, and couldn't find a store locally (with in an hour's drive) that carries the colour I'm using. I tried several large mail-order businesses. None of them had it. I was at the Cascade web-site looking up every retailer they listed in New England, now, and was having no luck. When I was about to resign myself to frogging and starting over in a new colour I got an e-mail from Sue at Lamb's Ear Yarns (where I bought the original yarn). She had found a bag of the yarn in the back of the store somewhere. It was the same lot and everything! Thank goodness! I don't think I could have handled having to frog it!