Starfish come in many sizes and colours. I have knitted my pattern using doubleknit wool, and 3mm needles, or 4ply wool and 2.5mm needles. I don't think there is a wrong size for a starfish.
The embroidery on the starfish was a bit of an afterthought. The pattern contains all the knitting details, and how to link to my blog where I demonstrate how to add the spots using a french knot.
And if you would like some sea creatures already knitted up, then visit my Etsy shop at https://www.etsy.com/shop/GinxCraft where I have some seaside sets for sale.