Expect 10% off tops. Can always book now and adjust later. Just undersntand the discount is maybe $20 a night off a $200/nt room. Still going to pony up some dollars.
Most folks can always stay a couple days onsite and a couple days off just to get the onsite experience. Most hotel amenities are open to the public. 90%-95% of the Disney experience can be had with offsite hotel (imho).