I can't comment definitively on the length of bows, but here's a thread that goes into it a little:
bow length
As far as hair goes, most will tell you that black hair "grabs" the string better, but white hair will offer a more refined tone. A lot of players ask for a mix of the two.
Stay away from the synthetic hair if you can.
And yes, you will need rosin for black hair.
Hope this helps.