Yes get a needle gauge. That will help you with 'what the heck size is this?' problem. I've not had that problem before but I can see myself having the problem if I buy second hand needles to figure out what size they are.
I buy these http://www.skacelknitting.com/s.nl/sc.2/category.22/.f
best circulars I ever used. The cord doesn't get all squirrely on me like some of the other circulars I've used. It's definately worth the price for me.