That's similar to what I use, except I use a multiple of 10. I usually co 100 st for an adult hat (I think I knit about 19 st/4 "). I also do the decrease in the same way.
I find if you knit longer before the decrease, you get a better looking hat. For an adult hat, I usually knit about 9" before the decrease.
I personally wouldn't use fun fur; I hate the stuff. Keep in mind if you strand it with your other yarn for the brim, you will be altering your gauge, and fun fur by itself won't hold the roll.
I never use circulars for hats, I find that they feel toooooooo short; I do however use dpn because seams on hats look bad, and on a rolled brim, especially bad.