I recently repainted an old explorer, only I don't like how it came out, and intend to repaint it again. I just had the thought of routing the body to add a single coil in, because it only has one humbucker, that's in the bridge position. What would I need to do to add a single coil in? Would I need to add in another 2 knobs? How do I put in the 3 way toggle switch? I was thinking about replacing the Humbucker aswell if money allows.

Sorry if this is vague.
Well you'd have to route for the singlecoil aswell as drill a canal for the wires to go into the control cavity. 1 vol and 1 tone should work fine, but knobs are always fun to have... the 3-way could be a hassle without the proper tools, if you want it clean that is.