I made a boatload of these (over 200) to totally trick out my groovyghan which can be seen here.

I am making these with a 4.5 mm hook and worsted weight yarn; I have detailed the specifics of how to make these in this blog post.

Unless you crochet very tightly, I wouldn’t recommend using a hook larger than 4.5 mm for worsted weight.

I would use two strands of yarn (or a bulky/chunky weight) if if you wanted “bigger” curlicues.