I suppose your off road ability will be limited by your tire choices and your willingness to rash a $550 wheel.
As far as big brakes, anything is possible. My guess on the Alcon kit is it's going to be north of $5000.
I have a set of AP racing 6 pots in the garage and two sets of rotors 14" and 13.5" might be interesting to measure out.
The D110 calipers are mounted with bolts through two eye tabs and whatever 6 pot caliper you get will likely be a radial mount. Axial to radial mount brackets are fairly easy to make. Selecting an appropriate two piece rotor will not be difficult with some so so accurate measurements with a steel scale. Oh and you might need a bigger master cylinder (I'm not sure what the surface area of the defender piston is).
I'll do it for $3500 shipped with a $600 deposit and a liability waiver for my bracket