This is probably the easiest stage of all, but don't rush it. Using Milliput, or whatever
material you intend to use instead, we're going to build a rough surface over the wireframes.
This will become a base we can then model the final surface over. You could simply model
the final surface straight off, but there's nothing solid to really get a hold of at the
moment, and adding an sub-layer remedies that.
The sub-layer really is very crude and simple. Take small, finger-sized knobs of putty and squash them into flat, tile-like shapes. Simply attach these to the wireframe, and embed the wire. The end result will be something that resembles a three-year-old's attempt at making a vase, but all the refinement comes with the next layer. I recommend doing the wall of the hoof first and letting it dry for a day. Then do the sole. The sole at this stage should be a completely flat base, with no attempt at realism.
It's difficult to see in the photographs, but try to keep the wall at the back, the heel, deliberately low, as this will later allow you more flexibility in putting the hoof on, and in flexing your hand up and down.
At this stage, trying your hooves on is critical, since this is the inside surface against which your fist will rest in the finished article. This is the stage at which to make things comfortable! When you fill in the sole, make sure the wire is covered and no sharp bits of solder are exposed.
Weight the hoof down with something heavy - if you did the wall first, that part of the hoof should now be very sturdy and able to take quite a substantial weight. The reason for using the plastic bag is so that the putty does not adhere to your worksurface. It will stick to the plastic instead: when the sole has dried, this should then be easy to peel away. Again, let it dry for a day before moving on.