You don’t need to do the chain 1 in Helen’s direction #4 - that would at the end of your first row if you were turning and making a second row of sc, which you’re not.
Here’s how I would go about the edging: Figure out the number of stitches along the edge you’re doing, let’s say it’s 64. 3 can go into 64 21 times, with one left over, so we know that we will pick up in 63 of those stitches (64 original st minus the one left over will give a number that can be evenly divided by 3 with no left over). You could also round up to picking up in 66 st, depending on how it’s looking as you’re going along, since you want to keep kind of a flat edge at this point.
Starting at your shoulder seam with WS facing, insert your hook into the first st where you want to pick up. Leave yourself a nice tail, 6 or 8 inches, have your yarn in back with tail to the right and YO the hook, draw it through the knitting to the front, YO again and pull that through the first loop on your hook. This is one sc. *Insert your hook into the next st to the left where you want to pick up (since you are picking up in every st but 1 this should be the very next st directly to the left of where you just made a st), YO the hook, draw it through the knitting to the front, YO again and pull that throught both loops on your hook. Repeat from * all the way around til you are back to the beginning. Somewhere along there you will either skip one st (to make 63) or pick up an extra 2 (to make 66) - you will have to see how it looks. When you get back to the stitch you started with you will join with a slip stitch (not the same as sl st in knitting) - you will insert your needle under the chain on the top of the first stitch you made, YO and pull that through to the front and through the loop on the needle. That finishes the base row.
Turn your work, *chain 3, insert your hook into the 3rd sc base st, YO, pull that through to the front, YO again and pull that throught both loops on your hook. Chain 3 more, insert your needle under the chain on the top of the sc stitch you just made, YO and pull that through to the front and through the loop on the needle. Repeat from * all the way around til you’re back to the original chain 3, at which point you would insert your needle into the base of the chain 3, YO and draw that to the front and the loop on your hook. Fasten off and weave in your ends.
With all that said, I’m thinking this is kind of a modified picot - usually your chains are anchored by a sl st OR a sc, not both, so I’m thinking this is making an edging with a protrusion (for lack of a better word in my just-woke-up-mind) in between the half loops of the chain sts.