If you are moving in the direction of establishing a permanent connection to the Internet, I would also suggest that you get
The Book of PF:
http://nostarch.com/pf.htm
By having a permanent connection, you will have to put serious thought into how to protect any device exposed, & studying
pf(4) is a
very good place to begin. Hansteen wrote a preliminary tutorial which is still available online:
http://www.bgnett.no/~peter/pf/
I would highly suggest reading both.