I've done both. If you want spl you should leave out the divieder. As for the port I like to have two ports on opposite sides of the box. Thats just me though.
I have the same opinion. Thats why most of my boxes have a divider. The box I have now is a lot louder since it doesn't have the divider. Its really just your preference. If one sub fails you should have enough time to turn it down before damaging the other one.