The DD facia will be slightly too large for the unit as it is made for two SD units with a separator. When you cut the separator out you increase the size of the hole by that much over a DD spec. Looks a bit of a mess to start with . I've got a hold of some leather that nearly matches the alezan interior which I intend to fit into the gap, not got round to doing it yet tho.
I doubt you'll use the cage in the install (I didn't) as the central console has its own cage, the DD facia will slot into it nicely.
The RCA plugs from the ICT loom should plug into the cable supplied with the Pioneer kit. That is unless Pioneer pull the same trick with you as they played with me and supply a cable without speaker RCA outputs (only sub) and loudly claim this model doesn't require the additional outputs while putting their fingers in their ears and humming loudly over any response I might make. Their customer service sucks. Don't even bother, seriously.
I paid a pro £45 to splice in RCA connectors from the higher level outputs. He also provided signal boosters for the lines and my god do they boost the signal. If I turn the bass and volume up (not all the way up, I like my bones to remain in a solid state) the sub stops being sound and starts being a strange feeling of being assaulted by the air from all sides at once.