If you're trading in RCI Weeks, I would start an Ongoing Search now if you can.
If you have a particular resort where you'd like to stay -- like BWV or BCV because of the Flower & Garden Festival at Epcot -- I would only list those resorts. If you get closer to arrival and you're afraid you won't get anything, you can broaden your search without losing your early search priority. But if you start out with a broad search, you're going to get SSR.
You can check the TUG Sightings board for more accurate info, but my sense is that DVC is doing their bulk deposits around 5-7 months from arrival. For the last year or more, they have been depositing almost exclusively one bedrooms.
If you're trading a fixed-grid system like Wyndham or Hilton, a DVC exchange is pretty doable. If you're trading based on TPU, you'll have to research that and be sure you have enough trading power.
May is a great time of the year for WDW! Have a great trip.