Body is Crocheted in the round continuously not joined. The yellow belly accents are crocheted in rows.
gauge and hook size is not particularly important as long as you crochet in a consistent size and use yarns of the same size and in reasonable balance with your hook size the plushie should turn out right.
I used Red Heart Super Saver in Glow Worm for the main body and scraps of a yellow I had for the belly and tail.