biggest realistic box would be 5 cubes
for what your doing see my build tread: http://www.grandprixforums.net/quiet-1-a-54698.html
personally i would get your electrical in order 1st. HO alt 2 runs of 0/1 pos and neg
then i would start looking at a more powerfull amp due to rise you won't get the right power
as far as box goes tune in the mid to low 30s (works good for me) if your going to do more than the rms make the box slightly smaller for better sub control