If AP rates do not come out, will you still stay at the resort paying full price?
If so, go ahead & book now. If not, then there is no sense in booking now because already having a room reservation does not increase your chances of getting the AP rate when (if) it comes out. In fact, it can have a negative impact on whether AP rates come out at all. If there are already enough bookings then there will be no AP rates released. Late March is a popular time of year so it is possible that they won't be released. But you never know.
As for cancellation, if you are booking a room-only reservation, then there is a 5 day cancellation policy, so you should be fine there.