I've already walked dozens down my line of thought, but I think providing a little step-by-step is worth it. First off, the construction in theory is a snap, but because we're working from the bottom up, we need to cast on for the entire length of the bottom of the pocket first, then decrease so that the inside pocket is a triangular shape that merges into the body of the cardigan seamlessly. In the pattern, I recommended the use of double pointed needles for the pocket stitches (you will need 5 DPNs if you go this route; two to hold each of the pocket stitches, half the count on each needle & a needle to actually knit with) though you could certainly use circular needles here also. In fact, when I was working the pattern out, I used long circs and it went very smoothly.
The reason we're even considering this fussiness is because the first few rows of the pockets are going to be very tight and hard to manage. Have you ever joined sleeves on a bottom up sweater and wanted to strangle someone every time you neared the underarms for the first inch or so after the join? Me too. That's sort of what we're dealing with for the first inch of the pockets. After that inch though, there's no reason you can't ditch the extra needles and transfer the stitches back onto the working needles.
SO, this is what's happening after the stitches are cast on and marked for decreases: on the next WS row, when you reach the cast on stitches, transfer them to your preferred spare needles. If using DPNs, they will be split evenly and you will use a third needle to knit, if using long circs, you will simply knit, slipping the markers. Since we're dealing with garter stitch, we're going on this way until it's time for the decreases, and by this point it should be safe to transfer the stitches back onto the working needles.
I sure hope this helps those who are just kind of staring at the pattern blankly or crying over a strip of garter stitch full of DPNs with no idea how to proceed.