The highest level of bow is indeed 28.

All of assistant skills can be used with a bow.
Offensive skills with a bow: Stone Ball Attack (fire magical skill), Arrow Rain (Volley, quest skill)

How you train, how you add the points after every level, which weapon you will use are up to you.

I have only an advice: Get all assistant skills first in the beginning. They would be very good for burst/goddess training, so you can train really fast.