You only need to be a little more than the diameter of the port away from the wall. Your 7-10 inches should be fine. Note that the cylinder downfire subs have a bottom plate in front of the ports that is much closer than 7" and it uses 3" ports.

I am making my own subwoofers using two 12" AV12s. I think this is the best way to go if you don't mind getting dirty.

Also, You can't have too much bass as someone mentioned. You just need to level set using an spl meter like any other speaker.