RE: best time to start a food plot?
If your ground isn't frozen, you can always disc now and spread lime now to let it really leech in. The best time to lime is always yesterday. Get a soil test done first, you can send it to Mossy Oak, or a local testing facility and find out what kind of fertilizer and lime you need.
They can be very rewarding, and they can be a lot of work and $$$. Check out the wildlife management forum here, as well as the qdma forums. QDMA has probably the best collection of info on this that I have found.