I started installing my ProComp but stopped because of the time it was taking. It took me about 4-hrs to get to the point of dropping the front diff. On the Armada, the rear is as intense as the front so I was worried that I might not get it done before Monday so I stopped at that point and took it into Custom Offroad. It took them a day for the front and a day for the rear.
The Titan is different. It takes a good part of a day for the front but the rear is much, much easier and can be done within a couple hours. So I'm guessing a Titan might be able to be done in about 9-12hrs.
You cannot stack a spacer on top of the ProComp spacer, it's a huge liability and voids the warranties. Instead, you get some SAW's or Radflos from PRG and adjust them for any additional lift that you want to add.
Those Mud Grapplers should fit fine and the pinchweld mod is easy enough to do if necessary.