Thank you both - I;ve just noticed the pattern says 2ply of worsted on US size 11needles or 1ply on US size 8 which to me would suggest an aran on size 8 (5mm) or a chunky on size 11 (6.5 mm) ? there isn't a tension guide
I'm a Hooker, not a knitter, and I imagine you need two strands for a large crown for sturdiness. And to make it quicker to knit!
So yes, a chunky on the larger needles and Aran on the smaller ones - they look to be similar to the hook sizes I would expect. i would go slightly smaller on hook size to make it a firmer fabric if necessary, I don't know if this is the same for knitting.
Looking closely at the instructions I don't think it matters. You don't cast on the stitches for the circumference of the crown, just for the width and then you make it as long as you need it to be. As Soupy said you probably want 2 strands to give it a bit of body and help the points to stand upright.