Good choice on the resort. It gets nothing but great reviews and I have toured the property however I've never stayed there. I have stayed at one of Ginns other properties, the Hammock Beach resort, just south of Saint Augustine. I've stayed at many 4 and 5* resorts, and not many compare with it. One other thing, Reunion is very Resort"ish", in fact it will probably have more of a resort feel then many of the onsite properties.
As for renting from the owner, research what you're getting. Many people, even owners, have posted stating the Ginn makes it difficult to rent the units without using there program. All Ginn resorts, for example, operate as a cashless society. In other words, all purchases must be made with your room key, NO CASH. There have been varying reports that if you rent from the owner, the owner will have to keep track of what you spent, and bill you. This could be more hassel than it's worth. Also to the best of my knowledge, and this only affects large families, if you rent from an owner only 4 per villa can use the waterpark free, the rest pay $10/day. That restriction doesn't apply when renting through Ginn.
It may be worth it to check around, perhaps even call Ginn direct. Pricing varies and some great deals can often be found on direct rentals if you look hard enough.
Jim