I think either way is fine. I've read that you should seam from the cuff to the armpit so you don't have to fudge to even out the stitches at the cuff (which may look sloppy). But doing it this way can get a little tricky at the armpit if you've already seamed the sides. I think this is why some people say to seam from the armpit to the cuff. I've done it both ways, and I don't think it makes any difference.
I've seen people on this board substitute both Lion Jiffy and Wool-Ease Chunky to make this sweater. You should also check on Elann for chunky superwash wools. Right now they have Debbie Bliss Merino Chunky which they have listed as machine washable. It's a bit pricey though. Or what about Paton's Shetland Chunky? I've never used that, but they have it on Joanns.com, and I bet you could get gague with it. They have lots of colors too.
I really liked the microspun. It was the only bright colored sport weight I could find at Michael's. I was a bit nervous about it b/c I've read so many posts about it being "splitty" and a pain to work with. I didn't think that at all. I loved knitting with it.