Mr. Roper's discovery suggestions are always very valuable. But if you want to develop a thorough, thoughtful and effective program of discovery, go to a good academic law library and look at the multi-volume treatise Bender's Forms of Discovery.
Benders gives examples of interrogatories, requests for admissions, requests for production and deposition questions covering almost any possible subject.
While these will not be tailored to a foreclosure defense, if you look carefully and take time, you will begin to see what kinds of questions can be effective and what kinds of objections can be reasonably interposed. This reference is also helpful in preparing and arguing a motion to compel.
If you don't set foot in a legal library you have no hope.