The chain arches that form the main part get larger as you work towards the top, but I wouldn't do that again, since I ended up decreasing at the top to cinch it in a little. That's partly because of how I wanted the strap, but next time I'd make the bag part the same height, but more narrow. The mesh stitch used works well because it's stretchy and not bulky, so I'd probably keep that but just use smaller meshes.
I used mercerized cotton yarn that is fingering weight and a 3 1/2mm (US size E) crochet hook. The pattern called for postal twine and a US size F hook. It really doesn't matter what's used to make this--any yarn and an appropriate hook will work.
I'm quite pleased with my new bag--I think I'll use it a lot.