You can make this spider any size you like! The size of the spider will depend on the yarn and hook used.
Thinner yarn/smaller hook = smaller spider. Thicker yarn/larger hook = larger spider.
The spider shown was made using a 3.50mm hook with Premier Big Ball yarn. Finished size is 3".
This pattern does not require a specific yarn or hook. Just make sure that the hook you use is a size or two smaller than the recommended hook for that yarn.
Gauge is not important. Be sure to crochet tightly enough so stuffing does not show through the holes. The amount of stuffing needed will depend on the size of the spider you make.