14" or port would be great in .75 cube box. im currently building a box for 2 of these and talking with sean of sundown, he says they do best in a .75 cube box
big 3 and a extra battery (a good sized one) should be ok. i wouldnt buy a z unless you put some power to it. if you want to be cheap on the amp and electrical then get some sa's (which by the way are my favorite woofer i have ever used)
I have a skar 1500 on my z and I need an alt. no matter what your gonna need to upgrade your electrical. plus with stock electrical that bc2k insnt going to put out rated and then also box rise
pretty much its all on you. It really all depends and how you set the amp up and how you are with the volume. im going to be running mine off of a 3.5k soon
theres guys running 3.5Ks and 5Ks on them daily. its just on how you adjust and listen to it. I have mine on a skar 1500 right now and from playing it for a few weeks I need atleast a 3-3.5k so make this thing loud. the 1500rms I think is a load of crap. I know its just a safety measure but it needs twice that