Unless you buy direct from Disney AND your guide is able to work some magic, you may not be able to get a May reservation, since that is only 2 months away. You might, since some parts of May are not super demand times, but I wouldn't count on it. DVC is best used to book 11-7 months out from your trip. Availability gets very limited as you get closer, as the intent of the DVC resorts is to run close to 100% occupancy at all times if possible.
If you buy a resale, I would think you would have no chance of finding a May reservation - at least not all at one resort for more than 3-4 days.
Also it might be best to plan a trip where you rent points and stay in DVC accommodations before committing to purchase. You may find that you don't even like staying DVC - it's not the same as staying on cash.