1) When can I expect my pāpale niu?
--You should receive your order within 1-3 weeks. 

2) How do I figure out my head measurement?

Use a measuring tape and follow the picture below.  (pic below is 21 inches)

If you don't have a measuring tape, use a floss or string and follow pic below. Mark measurement with a pen. Measure with a ruler from one end to the pen mark.