I have a buddy who used to have a ton of them...if I remember correctly its .5 cubes ported. Tune to whatever. But stay small on the port area, maybe 8sq in per cube. They like to get sloppy with any more.
Yes lower...tuning is also very vehicle and driver dependent. My box is tuned to 26...but I can still kill the 40's. My last few were tuned to 35, 32...but my subs seemed to lack in the low end dept. Threw this one in there and couldn't be happier.
That amp puts out a hair over 3k at 12v at 1ohm...are you going to be able to hold a steady 12v? If not the rms is going to decrease by quite bit. And add box rise on top of that. You're sub will be fine...just keep an eye on it and know your limits.